left-hand side of a production rule, the indices $a_1$, \ldots, $a_n$ are
variables which vary over all nonterminal and terminal symbols, and the
variables may also appear on the right-hand side in place of a nonterminal.
-Such a rule stands for a family of rules, in each variable is replaced by
-each possible simple nonterminal or terminal symbol.
+Such a rule stands for a family of rules, in which each variable is replaced
+by each possible simple nonterminal or terminal symbol.
The letter $\epsilon$ denotes the empty nonterminal
\begin{quote}
and the variables may also appear on the right-hand side
in place of a nonterminal.
Such a rule stands for a family of rules,
-in each variable is replaced by
+in which each variable is replaced by
each possible simple nonterminal or terminal symbol.
.PP
The letter \*e denotes the empty nonterminal