+whose colour can be determined trivially. In \q{Normal} and \q{Hard}
+modes, you will have to use increasingly complex logic to deduce the
+colour of some regions. However, it will always be possible without
+having to guess or backtrack.
+
+\lcont{
+
+In \q{Unreasonable} mode, the program will feel free to generate
+puzzles which are as hard as it can possibly make them: the only
+constraint is that they should still have a unique solution. Solving
+Unreasonable puzzles may require guessing and backtracking.
+
+}
+
+
+\C{loopy} \i{Loopy}
+
+\cfg{winhelp-topic}{games.loopy}
+
+You are given a grid of dots, marked with yellow lines to indicate
+which dots you are allowed to connect directly together. Your aim is
+to use some subset of those yellow lines to draw a single unbroken
+loop from dot to dot within the grid.
+
+Some of the spaces between the lines contain numbers. These numbers
+indicate how many of the lines around that space form part of the
+loop. The loop you draw must correctly satisfy all of these clues to
+be considered a correct solution.
+
+In the default mode, the dots are arranged in a grid of squares;
+however, you can also play on triangular or hexagonal grids, or even
+more exotic ones.
+
+Credit for the basic puzzle idea goes to \i{Nikoli}
+\k{nikoli-loopy}.
+
+Loopy was originally contributed to this collection by Mike Pinna,
+and subsequently enhanced to handle various types of non-square grid
+by Lambros Lambrou.
+
+\B{nikoli-loopy}
+\W{http://www.nikoli.co.jp/puzzles/3/index-e.htm}\cw{http://www.nikoli.co.jp/puzzles/3/index-e.htm}
+(beware of Flash)
+
+\H{loopy-controls} \i{Loopy controls}
+
+\IM{Loopy controls} controls, for Loopy
+
+Click the left mouse button on a yellow line to turn it black,
+indicating that you think it is part of the loop. Click again to
+turn the line yellow again (meaning you aren't sure yet).
+
+If you are sure that a particular line segment is \e{not} part of
+the loop, you can click the right mouse button to remove it
+completely. Again, clicking a second time will turn the line back to
+yellow.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{loopy-parameters} \I{parameters, for Loopy}Loopy parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid, measured in number of regions across and down. For
+square grids, it's clear how this is counted; for other types of
+grid you may have to think a bit to see how the dimensions are
+measured.
+
+\dt \e{Grid type}
+
+\dd Allows you to choose between a selection of types of tiling.
+Some have all the faces the same but may have multiple different
+types of vertex (e.g. the \e{Cairo} or \e{Kites} mode); others have
+all the vertices the same but may have different types of face (e.g.
+the \e{Great Hexagonal}). The square, triangular and honeycomb grids
+are fully regular, and have all their vertices \e{and} faces the
+same; this makes them the least confusing to play.
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle.
+\#{FIXME: what distinguishes Easy, Medium, and Hard? In particular,
+when are backtracking/guesswork required, if ever?}
+
+
+\C{inertia} \i{Inertia}
+
+\cfg{winhelp-topic}{games.inertia}
+
+You are a small green ball sitting in a grid full of obstacles. Your
+aim is to collect all the gems without running into any mines.
+
+You can move the ball in any orthogonal \e{or diagonal} direction.
+Once the ball starts moving, it will continue until something stops
+it. A wall directly in its path will stop it (but if it is moving
+diagonally, it will move through a diagonal gap between two other
+walls without stopping). Also, some of the squares are \q{stops};
+when the ball moves on to a stop, it will stop moving no matter what
+direction it was going in. Gems do \e{not} stop the ball; it picks
+them up and keeps on going.
+
+Running into a mine is fatal. Even if you picked up the last gem in
+the same move which then hit a mine, the game will count you as dead
+rather than victorious.
+
+This game was originally implemented for Windows by Ben Olmstead
+\k{bem}, who was kind enough to release his source code on request
+so that it could be re-implemented for this collection.
+
+\B{bem} \W{http://xn13.com/}\cw{http://xn13.com/}
+
+\H{inertia-controls} \i{Inertia controls}
+
+\IM{Inertia controls} controls, for Inertia
+\IM{Inertia controls} keys, for Inertia
+\IM{Inertia controls} shortcuts (keyboard), for Inertia
+
+You can move the ball in any of the eight directions using the
+numeric keypad. Alternatively, if you click the left mouse button on
+the grid, the ball will begin a move in the general direction of
+where you clicked.
+
+If you use the \q{Solve} function on this game, the program will
+compute a path through the grid which collects all the remaining
+gems and returns to the current position. A hint arrow will appear
+on the ball indicating the direction in which you should move to
+begin on this path. If you then move in that direction, the arrow
+will update to indicate the next direction on the path. You can also
+press Space to automatically move in the direction of the hint
+arrow. If you move in a different direction from the one shown by
+the arrow, the hint arrows will stop appearing because you have
+strayed from the provided path; you can then use \q{Solve} again to
+generate a new path if you want to.
+
+All the actions described in \k{common-actions} are also available.
+In particular, if you do run into a mine and die, you can use the
+Undo function and resume playing from before the fatal move. The
+game will keep track of the number of times you have done this.
+
+\H{inertia-parameters} \I{parameters, for Inertia}Inertia parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+
+\C{tents} \i{Tents}
+
+\cfg{winhelp-topic}{games.tents}
+
+You have a grid of squares, some of which contain trees. Your aim is
+to place tents in some of the remaining squares, in such a way that
+the following conditions are met:
+
+\b There are exactly as many tents as trees.
+
+\b The tents and trees can be matched up in such a way that each
+tent is directly adjacent (horizontally or vertically, but not
+diagonally) to its own tree. However, a tent may be adjacent to
+other trees as well as its own.
+
+\b No two tents are adjacent horizontally, vertically \e{or
+diagonally}.
+
+\b The number of tents in each row, and in each column, matches the
+numbers given round the sides of the grid.
+
+This puzzle can be found in several places on the Internet, and was
+brought to my attention by e-mail. I don't know who I should credit
+for inventing it.
+
+\H{tents-controls} \i{Tents controls}
+
+\IM{Tents controls} controls, for Tents
+
+Left-clicking in a blank square will place a tent in it.
+Right-clicking in a blank square will colour it green, indicating
+that you are sure it \e{isn't} a tent. Clicking either button in an
+occupied square will clear it.
+
+If you \e{drag} with the right button along a row or column, every
+blank square in the region you cover will be turned green, and no
+other squares will be affected. (This is useful for clearing the
+remainder of a row once you have placed all its tents.)
+
+You can also use the cursor keys to move around the grid. Pressing the
+return key over an empty square will place a tent, and pressing the
+space bar over an empty square will colour it green; either key will
+clear an occupied square.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{tents-parameters} \I{parameters, for Tents}Tents parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. More difficult
+puzzles require more complex deductions, but at present none of the
+available difficulty levels requires guesswork or backtracking.
+
+
+\C{bridges} \i{Bridges}
+
+\cfg{winhelp-topic}{games.bridges}
+
+You have a set of islands distributed across the playing area. Each
+island contains a number. Your aim is to connect the islands
+together with bridges, in such a way that:
+
+\b Bridges run horizontally or vertically.
+
+\b The number of bridges terminating at any island is equal to the
+number written in that island.
+
+\b Two bridges may run in parallel between the same two islands, but
+no more than two may do so.
+
+\b No bridge crosses another bridge.
+
+\b All the islands are connected together.
+
+There are some configurable alternative modes, which involve
+changing the parallel-bridge limit to something other than 2, and
+introducing the additional constraint that no sequence of bridges
+may form a loop from one island back to the same island. The rules
+stated above are the default ones.
+
+Credit for this puzzle goes to \i{Nikoli} \k{nikoli-bridges}.
+
+Bridges was contributed to this collection by James Harvey.
+
+\B{nikoli-bridges}
+\W{http://www.nikoli.co.jp/puzzles/14/index-e.htm}\cw{http://www.nikoli.co.jp/puzzles/14/index-e.htm}
+
+\H{bridges-controls} \i{Bridges controls}
+
+\IM{Bridges controls} controls, for Bridges
+
+To place a bridge between two islands, click the mouse down on one
+island and drag it towards the other. You do not need to drag all
+the way to the other island; you only need to move the mouse far
+enough for the intended bridge direction to be unambiguous. (So you
+can keep the mouse near the starting island and conveniently throw
+bridges out from it in many directions.)
+
+Doing this again when a bridge is already present will add another
+parallel bridge. If there are already as many bridges between the
+two islands as permitted by the current game rules (i.e. two by
+default), the same dragging action will remove all of them.
+
+If you want to remind yourself that two islands definitely \e{do
+not} have a bridge between them, you can right-drag between them in
+the same way to draw a \q{non-bridge} marker.
+
+If you think you have finished with an island (i.e. you have placed
+all its bridges and are confident that they are in the right
+places), you can mark the island as finished by left-clicking on it.
+This will highlight it and all the bridges connected to it, and you
+will be prevented from accidentally modifying any of those bridges
+in future. Left-clicking again on a highlighted island will unmark
+it and restore your ability to modify it.
+
+You can also use the cursor keys to move around the grid: if possible
+the cursor will always move orthogonally, otherwise it will move
+towards the nearest island to the indicated direction. Pressing the
+return key followed by a cursor key will lay a bridge in that direction
+(if available); pressing the space bar followed by a cursor key will
+lay a \q{non-bridge} marker.
+
+You can mark an island as finished by pressing the return key twice.
+
+Violations of the puzzle rules will be marked in red:
+
+\b An island with too many bridges will be highlighted in red.
+
+\b An island with too few bridges will be highlighted in red if it
+is definitely an error (as opposed to merely not being finished
+yet): if adding enough bridges would involve having to cross another
+bridge or remove a non-bridge marker, or if the island has been
+highlighted as complete.
+
+\b A group of islands and bridges may be highlighted in red if it is
+a closed subset of the puzzle with no way to connect it to the rest
+of the islands. For example, if you directly connect two 1s together
+with a bridge and they are not the only two islands on the grid,
+they will light up red to indicate that such a group cannot be
+contained in any valid solution.
+
+\b If you have selected the (non-default) option to disallow loops
+in the solution, a group of bridges which forms a loop will be
+highlighted.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{bridges-parameters} \I{parameters, for Bridges}Bridges parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+\dt \e{Difficulty}
+
+\dd Difficulty level of puzzle.
+
+\dt \e{Allow loops}
+
+\dd This is set by default. If cleared, puzzles will be generated in
+such a way that they are always soluble without creating a loop, and
+solutions which do involve a loop will be disallowed.
+
+\dt \e{Max. bridges per direction}
+
+\dd Maximum number of bridges in any particular direction. The
+default is 2, but you can change it to 1, 3 or 4. In general, fewer
+is easier.
+
+\dt \e{%age of island squares}
+
+\dd Gives a rough percentage of islands the generator will try and
+lay before finishing the puzzle. Certain layouts will not manage to
+lay enough islands; this is an upper bound.
+
+\dt \e{Expansion factor (%age)}
+
+\dd The grid generator works by picking an existing island at random
+(after first creating an initial island somewhere). It then decides
+on a direction (at random), and then works out how far it could
+extend before creating another island. This parameter determines how
+likely it is to extend as far as it can, rather than choosing
+somewhere closer.
+
+High expansion factors usually mean easier puzzles with fewer
+possible islands; low expansion factors can create lots of
+tightly-packed islands.
+
+
+\C{unequal} \i{Unequal}
+
+\cfg{winhelp-topic}{games.unequal}
+
+You have a square grid; each square may contain a digit from 1 to
+the size of the grid, and some squares have clue signs between
+them. Your aim is to fully populate the grid with numbers such that:
+
+\b Each row contains only one occurrence of each digit
+
+\b Each column contains only one occurrence of each digit
+
+\b All the clue signs are satisfied.
+
+There are two modes for this game, \q{Unequal} and \q{Adjacent}.
+
+In \q{Unequal} mode, the clue signs are greater-than symbols indicating one
+square's value is greater than its neighbour's. In this mode not all clues
+may be visible, particularly at higher difficulty levels.
+
+In \q{Adjacent} mode, the clue signs are bars indicating
+one square's value is numerically adjacent (i.e. one higher or one lower)
+than its neighbour. In this mode all clues are always visible: absence of
+a bar thus means that a square's value is definitely not numerically adjacent
+to that neighbour's.
+
+In \q{Trivial} difficulty level (available via the \q{Custom} game type
+selector), there are no greater-than signs in \q{Unequal} mode; the puzzle is
+to solve the \i{Latin square} only.
+
+At the time of writing, the \q{Unequal} mode of this puzzle is appearing in the
+Guardian weekly under the name \q{\i{Futoshiki}}.
+
+Unequal was contributed to this collection by James Harvey.
+
+\H{unequal-controls} \i{Unequal controls}
+
+\IM{Unequal controls} controls, for Unequal
+
+Unequal shares much of its control system with Solo.
+
+To play Unequal, simply click the mouse in any empty square and then
+type a digit or letter on the keyboard to fill that square. If you
+make a mistake, click the mouse in the incorrect square and press
+Space to clear it again (or use the Undo feature).
+
+If you \e{right}-click in a square and then type a number, that
+number will be entered in the square as a \q{pencil mark}. You can
+have pencil marks for multiple numbers in the same square. Squares
+containing filled-in numbers cannot also contain pencil marks.
+
+The game pays no attention to pencil marks, so exactly what you use
+them for is up to you: you can use them as reminders that a
+particular square needs to be re-examined once you know more about a
+particular number, or you can use them as lists of the possible
+numbers in a given square, or anything else you feel like.
+
+To erase a single pencil mark, right-click in the square and type
+the same number again.
+
+All pencil marks in a square are erased when you left-click and type
+a number, or when you left-click and press space. Right-clicking and
+pressing space will also erase pencil marks.
+
+As for Solo, the cursor keys can be used in conjunction with the digit
+keys to set numbers or pencil marks. You can also use the 'M' key to
+auto-fill every numeric hint, ready for removal as required, or the 'H'
+key to do the same but also to remove all obvious hints.
+
+Alternatively, use the cursor keys to move the mark around the grid.
+Pressing the return key toggles the mark (from a normal mark to a
+pencil mark), and typing a number in is entered in the square in the
+appropriate way; typing in a 0 or using the space bar will clear a
+filled square.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{unequal-parameters} \I{parameters, for Unequal}Unequal parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Mode}
+
+\dd Mode of the puzzle (\q{Unequal} or \q{Adjacent})
+
+\dt \e{Size (s*s)}
+
+\dd Size of grid.
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. At Trivial
+level, there are no greater-than signs; the puzzle is to solve the
+Latin square only. At Recursive level (only available via the
+\q{Custom} game type selector) backtracking will be required, but
+the solution should still be unique. The levels in between require
+increasingly complex reasoning to avoid having to backtrack.
+
+
+
+\C{galaxies} \i{Galaxies}
+
+\cfg{winhelp-topic}{games.galaxies}
+
+You have a rectangular grid containing a number of dots. Your aim is
+to draw edges along the grid lines which divide the rectangle into
+regions in such a way that every region is 180\u00b0{-degree}
+rotationally symmetric, and contains exactly one dot which is
+located at its centre of symmetry.
+
+This puzzle was invented by \i{Nikoli} \k{nikoli-galaxies}, under
+the name \q{Tentai Show}; its name is commonly translated into
+English as \q{Spiral Galaxies}.
+
+Galaxies was contributed to this collection by James Harvey.
+
+\B{nikoli-galaxies} \W{http://www.nikoli.co.jp/en/puzzles/astronomical_show/}\cw{http://www.nikoli.co.jp/en/puzzles/astronomical_show/}
+
+\H{galaxies-controls} \i{Galaxies controls}
+
+\IM{Galaxies controls} controls, for Galaxies
+
+Left-click on any grid line to draw an edge if there isn't one
+already, or to remove one if there is. When you create a valid
+region (one which is closed, contains exactly one dot, is
+180\u00b0{-degree} symmetric about that dot, and contains no
+extraneous edges inside it) it will be highlighted automatically; so
+your aim is to have the whole grid highlighted in that way.
+
+During solving, you might know that a particular grid square belongs
+to a specific dot, but not be sure of where the edges go and which
+other squares are connected to the dot. In order to mark this so you
+don't forget, you can right-click on the dot and drag, which will
+create an arrow marker pointing at the dot. Drop that in a square of
+your choice and it will remind you which dot it's associated with.
+You can also right-click on existing arrows to pick them up and move
+them, or destroy them by dropping them off the edge of the grid.
+(Also, if you're not sure which dot an arrow is pointing at, you can
+pick it up and move it around to make it clearer. It will swivel
+constantly as you drag it, to stay pointed at its parent dot.)
+
+You can also use the cursor keys to move around the grid squares and
+lines. Pressing the return key when over a grid line will draw or
+clear its edge, as above. Pressing the return key when over a dot will
+pick up an arrow, to be dropped the next time the return key is
+pressed; this can also be used to move existing arrows around, removing
+them by dropping them on a dot or another arrow.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{galaxies-parameters} \I{parameters, for Galaxies}Galaxies parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. More difficult
+puzzles require more complex deductions, and the \q{Unreasonable}
+difficulty level may require backtracking.
+
+
+
+\C{filling} \i{Filling}
+
+\cfg{winhelp-topic}{games.filling}
+
+You have a grid of squares, some of which contain digits, and the
+rest of which are empty. Your job is to fill in digits in the empty
+squares, in such a way that each connected region of squares all
+containing the same digit has an area equal to that digit.
+
+(\q{Connected region}, for the purposes of this game, does not count
+diagonally separated squares as adjacent.)
+
+For example, it follows that no square can contain a zero, and that
+two adjacent squares can not both contain a one. No region has an
+area greater than 9 (because then its area would not be a single
+digit).
+
+Credit for this puzzle goes to \i{Nikoli} \k{nikoli-fillomino}.
+
+Filling was contributed to this collection by Jonas K\u00F6{oe}lker.
+
+\B{nikoli-fillomino}
+\W{http://www.nikoli.co.jp/en/puzzles/fillomino/}\cw{http://www.nikoli.co.jp/en/puzzles/fillomino/}
+
+\H{filling-controls} \I{controls, for Filling}Filling controls
+
+To play Filling, simply click the mouse in any empty square and then
+type a digit on the keyboard to fill that square. By dragging the
+mouse, you can select multiple squares to fill with a single keypress.
+If you make a mistake, click the mouse in the incorrect square and
+press 0, Space, Backspace or Enter to clear it again (or use the Undo
+feature).
+
+You can also move around the grid with the cursor keys; typing a digit will
+fill the square containing the cursor with that number, or typing 0, Space,
+or Enter will clear it. You can also select multiple squares for numbering
+or clearing by using the return key, before typing a digit to fill in the
+highlighted squares (as above).
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{filling-parameters} \I{parameters, for Filling}Filling parameters
+
+Filling allows you to configure the number of rows and columns of the
+grid, through the \q{Type} menu.
+
+
+\C{keen} \i{Keen}
+
+\cfg{winhelp-topic}{games.keen}
+
+You have a square grid; each square may contain a digit from 1 to
+the size of the grid. The grid is divided into blocks of varying
+shape and size, with arithmetic clues written in them. Your aim is
+to fully populate the grid with digits such that:
+
+\b Each row contains only one occurrence of each digit
+
+\b Each column contains only one occurrence of each digit
+
+\b The digits in each block can be combined to form the number
+stated in the clue, using the arithmetic operation given in the
+clue. That is:
+
+\lcont{
+
+\b An addition clue means that the sum of the digits in the block
+must be the given number. For example, \q{15+} means the contents of
+the block adds up to fifteen.
+
+\b A multiplication clue (e.g. \q{60\times}), similarly, means that
+the product of the digits in the block must be the given number.
+
+\b A subtraction clue will always be written in a block of size two,
+and it means that one of the digits in the block is greater than the
+other by the given amount. For example, \q{2\minus} means that one
+of the digits in the block is 2 more than the other, or equivalently
+that one digit minus the other one is 2. The two digits could be
+either way round, though.
+
+\b A division clue (e.g. \q{3\divide}), similarly, is always in a
+block of size two and means that one digit divided by the other is
+equal to the given amount.
+
+Note that a block may contain more than one digit the same (provided
+the identical ones are not in the same row and column). This rule is
+precisely the opposite of the rule in Solo's \q{Killer} mode (see
+\k{solo}).
+
+}
+
+This puzzle appears in the Times under the name \q{\i{KenKen}}.
+
+
+\H{keen-controls} \i{Keen controls}
+
+\IM{Keen controls} controls, for Keen
+
+Keen shares much of its control system with Solo (and Unequal).
+
+To play Keen, simply click the mouse in any empty square and then
+type a digit on the keyboard to fill that square. If you make a
+mistake, click the mouse in the incorrect square and press Space to
+clear it again (or use the Undo feature).
+
+If you \e{right}-click in a square and then type a number, that
+number will be entered in the square as a \q{pencil mark}. You can
+have pencil marks for multiple numbers in the same square. Squares
+containing filled-in numbers cannot also contain pencil marks.
+
+The game pays no attention to pencil marks, so exactly what you use
+them for is up to you: you can use them as reminders that a
+particular square needs to be re-examined once you know more about a
+particular number, or you can use them as lists of the possible
+numbers in a given square, or anything else you feel like.
+
+To erase a single pencil mark, right-click in the square and type
+the same number again.
+
+All pencil marks in a square are erased when you left-click and type
+a number, or when you left-click and press space. Right-clicking and
+pressing space will also erase pencil marks.
+
+As for Solo, the cursor keys can be used in conjunction with the
+digit keys to set numbers or pencil marks. Use the cursor keys to
+move a highlight around the grid, and type a digit to enter it in
+the highlighted square. Pressing return toggles the highlight into a
+mode in which you can enter or remove pencil marks.
+
+Pressing M will fill in a full set of pencil marks in every square
+that does not have a main digit in it.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{keen-parameters} \I{parameters, for Keen}Keen parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Grid size}
+
+\dd Specifies the size of the grid. Lower limit is 3; upper limit is
+9 (because the user interface would become more difficult with
+\q{digits} bigger than 9!).
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. At Unreasonable
+level, some backtracking will be required, but the solution should
+still be unique. The remaining levels require increasingly complex
+reasoning to avoid having to backtrack.
+
+
+\C{towers} \i{Towers}
+
+\cfg{winhelp-topic}{games.towers}
+
+You have a square grid. On each square of the grid you can build a
+tower, with its height ranging from 1 to the size of the grid.
+Around the edge of the grid are some numeric clues.
+
+Your task is to build a tower on every square, in such a way that:
+
+\b Each row contains every possible height of tower once
+
+\b Each column contains every possible height of tower once
+
+\b Each numeric clue describes the number of towers that can be seen
+if you look into the square from that direction, assuming that
+shorter towers are hidden behind taller ones. For example, in a
+5\by\.5 grid, a clue marked \q{5} indicates that the five tower
+heights must appear in increasing order (otherwise you would not be
+able to see all five towers), whereas a clue marked \q{1} indicates
+that the tallest tower (the one marked 5) must come first.
+
+In harder or larger puzzles, some towers will be specified for you
+as well as the clues round the edge, and some edge clues may be
+missing.
+
+This puzzle appears on the web under various names, particularly
+\q{\i{Skyscrapers}}, but I don't know who first invented it.
+
+
+\H{towers-controls} \i{Towers controls}
+
+\IM{Towers controls} controls, for Towers
+
+Towers shares much of its control system with Solo, Unequal and Keen.
+
+To play Towers, simply click the mouse in any empty square and then
+type a digit on the keyboard to fill that square with a tower of the
+given height. If you make a mistake, click the mouse in the
+incorrect square and press Space to clear it again (or use the Undo
+feature).
+
+If you \e{right}-click in a square and then type a number, that
+number will be entered in the square as a \q{pencil mark}. You can
+have pencil marks for multiple numbers in the same square. A square
+containing a tower cannot also contain pencil marks.
+
+The game pays no attention to pencil marks, so exactly what you use
+them for is up to you: you can use them as reminders that a
+particular square needs to be re-examined once you know more about a
+particular number, or you can use them as lists of the possible
+numbers in a given square, or anything else you feel like.
+
+To erase a single pencil mark, right-click in the square and type
+the same number again.
+
+All pencil marks in a square are erased when you left-click and type
+a number, or when you left-click and press space. Right-clicking and
+pressing space will also erase pencil marks.
+
+As for Solo, the cursor keys can be used in conjunction with the
+digit keys to set numbers or pencil marks. Use the cursor keys to
+move a highlight around the grid, and type a digit to enter it in
+the highlighted square. Pressing return toggles the highlight into a
+mode in which you can enter or remove pencil marks.
+
+Pressing M will fill in a full set of pencil marks in every square
+that does not have a main digit in it.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{towers-parameters} \I{parameters, for Towers}Towers parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Grid size}
+
+\dd Specifies the size of the grid. Lower limit is 3; upper limit is
+9 (because the user interface would become more difficult with
+\q{digits} bigger than 9!).
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. At Unreasonable
+level, some backtracking will be required, but the solution should
+still be unique. The remaining levels require increasingly complex
+reasoning to avoid having to backtrack.
+
+
+\C{singles} \i{Singles}
+
+\cfg{winhelp-topic}{games.singles}
+
+You have a grid of white squares, all of which contain numbers. Your task
+is to colour some of the squares black (removing the number) so as to satisfy
+all of the following conditions:
+
+\b No number occurs more than once in any row or column.
+
+\b No black square is horizontally or vertically adjacent to any other black
+square.
+
+\b The remaining white squares must all form one contiguous region
+(connected by edges, not just touching at corners).
+
+Credit for this puzzle goes to \i{Nikoli} \k{nikoli-hitori} who call it
+\i{Hitori}.
+
+Singles was contributed to this collection by James Harvey.
+
+\B{nikoli-hitori}
+\W{http://www.nikoli.com/en/puzzles/hitori/index.html}\cw{http://www.nikoli.com/en/puzzles/hitori/index.html}
+(beware of Flash)
+
+\H{singles-controls} \i{Singles controls}
+
+\IM{Singles controls} controls, for Singles
+
+Left-clicking on an empty square will colour it black; left-clicking again
+will replace the number. Right-clicking will add a circle (useful for
+indicating that a cell is definitely not black).
+
+You can also use the cursor keys to move around the grid. Pressing the
+return or space keys will turn a square black or add a circle respectively,
+and pressing the key again will replace the number or remove the circle.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{singles-parameters} \I{parameters, for Singles}Singles parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle.
+
+
+\C{magnets} \i{Magnets}
+
+\cfg{winhelp-topic}{games.magnets}
+
+A rectangular grid has been filled with a mixture of magnets (that is,
+dominoes with one positive end and one negative end) and blank dominoes
+(that is, dominoes with two neutral poles).
+These dominoes are initially only seen in silhouette. Around the grid
+are placed a number of clues indicating the number of positive and
+negative poles contained in certain columns and rows.
+
+Your aim is to correctly place the magnets and blank dominoes such that
+all the clues are satisfied, with the additional constraint that no two
+similar magnetic poles may be orthogonally adjacent (since they repel).
+Neutral poles do not repel, and can be adjacent to any other pole.
+
+Credit for this puzzle goes to \i{Janko} \k{janko-magnets}.
+
+Magnets was contributed to this collection by James Harvey.
+
+\B{janko-magnets}
+\W{http://www.janko.at/Raetsel/Magnete/index.htm}\cw{http://www.janko.at/Raetsel/Magnete/index.htm}
+
+\H{magnets-controls} \i{Magnets controls}
+
+\IM{Magnets controls} controls, for Magnets
+
+Left-clicking on an empty square places a magnet at that position with
+the positive pole on the square and the negative pole on the other half
+of the magnet; left-clicking again reverses the polarity, and a third
+click removes the magnet.
+
+Right-clicking on an empty square places a blank domino there.
+Right-clicking again places two question marks on the domino, signifying
+\q{this cannot be blank} (which can be useful to note deductions while
+solving), and right-clicking again empties the domino.
+
+You can also use the cursor keys to move a cursor around the grid.
+Pressing the return key will lay a domino with a positive pole at that
+position; pressing again reverses the polarity and then removes the
+domino, as with left-clicking. Using the space bar allows placement
+of blank dominoes and cannot-be-blank hints, as for right-clicking.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{magnets-parameters} \I{parameters, for Magnets}Magnets parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares. There will be half \e{Width} \by \e{Height}
+dominoes in the grid: if this number is odd then one square will be blank.
+
+(Grids with at least one odd dimension tend to be easier to solve.)
+
+\dt \e{Difficulty}
+
+\dd Controls the difficulty of the generated puzzle. At Tricky level,
+you are required to make more deductions about empty dominoes and
+row/column counts.
+
+\dt \e{Strip clues}
+
+\dd If true, some of the clues around the grid are removed at generation
+time, making the puzzle more difficult.
+
+
+\C{signpost} \i{Signpost}
+
+\cfg{winhelp-topic}{games.signpost}
+
+You have a grid of squares; each square (except the last one)
+contains an arrow, and some squares also contain numbers. Your job
+is to connect the squares to form a continuous list of numbers
+starting at 1 and linked in the direction of the arrows \dash so the
+arrow inside the square with the number 1 will point to the square
+containing the number 2, which will point to the square containing
+the number 3, etc. Each square can be any distance away from the
+previous one, as long as it is somewhere in the direction of the
+arrow.
+
+By convention the first and last numbers are shown; one or more
+interim numbers may also appear at the beginning.
+
+Credit for this puzzle goes to \i{Janko} \k{janko-arrowpath}, who call it
+\q{Pfeilpfad} (\q{arrow path}).
+
+Signpost was contributed to this collection by James Harvey.
+
+\B{janko-arrowpath}
+\W{http://janko.at/Raetsel/Pfeilpfad/index.htm}\cw{http://janko.at/Raetsel/Pfeilpfad/index.htm}
+
+\H{signpost-controls} \I{controls, for Signpost}Signpost controls
+
+To play Signpost, you connect squares together by dragging from one
+square to another, indicating that they are adjacent in the
+sequence. Drag with the left button from a square to its successor,
+or with the right button from a square to its predecessor.
+
+If you connect together two squares in this way and one of them has
+a number in it, the appropriate number will appear in the other
+square. If you connect two non-numbered squares, they will be
+assigned temporary algebraic labels: on the first occasion, they
+will be labelled \cq{a} and \cq{a+1}, and then \cq{b} and \cq{b+1},
+and so on. Connecting more squares on to the ends of such a chain
+will cause them all to be labelled with the same letter.
+
+When you left-click or right-click in a square, the legal squares to
+connect it to will be shown.
+
+The arrow in each square starts off black, and goes grey once you
+connect the square to its successor. Also, each square which needs a
+predecessor has a small dot in the bottom left corner, which
+vanishes once you link a square to it. So your aim is always to
+connect a square with a black arrow to a square with a dot.
+
+To remove any links for a particular square (both incoming and
+outgoing), left-drag it off the grid. To remove a whole chain,
+right-drag any square in the chain off the grid.
+
+You can also use the cursor keys to move around the grid squares and
+lines. Pressing the return key when over a square starts a link
+operation, and pressing the return key again over a square will
+finish the link, if allowable. Pressing the space bar over a square
+will show the other squares pointing to it, and allow you to form a
+backward link, and pressing the space bar again cancels this.
+
+(All the actions described in \k{common-actions} are also available.)
+
+\H{signpost-parameters} \I{parameters, for Signpost}Signpost parameters
+
+These parameters are available from the \q{Custom...} option on the
+\q{Type} menu.
+
+\dt \e{Width}, \e{Height}
+
+\dd Size of grid in squares.
+
+\dt \e{Force start/end to corners}
+
+\dd If true, the start and end squares are always placed in opposite corners
+(the start at the top left, and the end at the bottom right). If false the start
+and end squares are placed randomly (although always both shown).