+/* Draw a rectangle outline, using the drawing API's draw_line. */
+void draw_rect_outline(drawing *dr, int x, int y, int w, int h,
+ int colour);
+
+/* Draw a set of rectangle corners (e.g. for a cursor display). */
+void draw_rect_corners(drawing *dr, int cx, int cy, int r, int col);
+
+void move_cursor(int button, int *x, int *y, int maxw, int maxh, int wrap);
+
+/* Used in netslide.c and sixteen.c for cursor movement around edge. */
+int c2pos(int w, int h, int cx, int cy);
+int c2diff(int w, int h, int cx, int cy, int button);
+void pos2c(int w, int h, int pos, int *cx, int *cy);
+
+/* Draws text with an 'outline' formed by offsetting the text
+ * by one pixel; useful for highlighting. Outline is omitted if -1. */
+void draw_text_outline(drawing *dr, int x, int y, int fonttype,
+ int fontsize, int align,
+ int text_colour, int outline_colour, char *text);
+/*
+ * dsf.c
+ */
+int *snew_dsf(int size);
+
+void print_dsf(int *dsf, int size);
+
+/* Return the canonical element of the equivalence class containing element
+ * val. If 'inverse' is non-NULL, this function will put into it a flag
+ * indicating whether the canonical element is inverse to val. */
+int edsf_canonify(int *dsf, int val, int *inverse);
+int dsf_canonify(int *dsf, int val);
+int dsf_size(int *dsf, int val);
+
+/* Allow the caller to specify that two elements should be in the same
+ * equivalence class. If 'inverse' is TRUE, the elements are actually opposite
+ * to one another in some sense. This function will fail an assertion if the
+ * caller gives it self-contradictory data, ie if two elements are claimed to
+ * be both opposite and non-opposite. */
+void edsf_merge(int *dsf, int v1, int v2, int inverse);
+void dsf_merge(int *dsf, int v1, int v2);
+void dsf_init(int *dsf, int len);
+
+/*
+ * tdq.c
+ */
+
+/*
+ * Data structure implementing a 'to-do queue', a simple
+ * de-duplicating to-do list mechanism.
+ *
+ * Specification: a tdq is a queue which can hold integers from 0 to
+ * n-1, where n was some constant specified at tdq creation time. No
+ * integer may appear in the queue's current contents more than once;
+ * an attempt to add an already-present integer again will do nothing,
+ * so that that integer is removed from the queue at the position
+ * where it was _first_ inserted. The add and remove operations take
+ * constant time.
+ *
+ * The idea is that you might use this in applications like solvers:
+ * keep a tdq listing the indices of grid squares that you currently
+ * need to process in some way. Whenever you modify a square in a way
+ * that will require you to re-scan its neighbours, add them to the
+ * list with tdq_add; meanwhile you're constantly taking elements off
+ * the list when you need another square to process. In solvers where
+ * deductions are mostly localised, this should prevent repeated
+ * O(N^2) loops over the whole grid looking for something to do. (But
+ * if only _most_ of the deductions are localised, then you should
+ * respond to an empty to-do list by re-adding everything using
+ * tdq_fill, so _then_ you rescan the whole grid looking for newly
+ * enabled non-local deductions. Only if you've done that and emptied
+ * the list again finding nothing new to do are you actually done.)
+ */
+typedef struct tdq tdq;
+tdq *tdq_new(int n);
+void tdq_free(tdq *tdq);
+void tdq_add(tdq *tdq, int k);
+int tdq_remove(tdq *tdq); /* returns -1 if nothing available */
+void tdq_fill(tdq *tdq); /* add everything to the tdq at once */
+
+/*
+ * laydomino.c
+ */
+int *domino_layout(int w, int h, random_state *rs);
+void domino_layout_prealloc(int w, int h, random_state *rs,
+ int *grid, int *grid2, int *list);