(calc-rewrite-selection): Make rules a local variable.

(calc-rewrite-selection): Make rules a local variable.

(calc-rewr-sel): New variable.
(calc-rewrite-selection, calc-locate-selection-marker, calc-rewrite):
Use the declared variable calc-rewr-sel instead of sel.

(math-rewrite):  Use let* to declare variables.

(math-mt-many): Declare it.

(math-rewrite-whole-expr): New variable.
(math-rewrite, math-rewrite-phase): Replace variable expr by declared
variable.

(math-import-list): Declare it.

(math-rewrite-heads-heads, math-rewrite-heads-skips)
(math-rewrite-heads-blanks ): New variables.
(math-rewrite-heads, math-rewrite-heads-rec): Replace variables heads,
skips and blanks by declared variables.

(math-regs, math-num-regs, math-prog-last, math-bound-vars)
(math-conds, math-copy-neg, math-rhs, math-pattern, math-remembering)
(math-aliased-vars): Declare them.

(math-rwcomp-subst-old, math-rwcomp-subst-new)
(math-rwcomp-subst-old-func, math-rwcomp-subst-new-func):
New variables.
(math-rwcomp-substitute, math-rwcomp-subst-rec): Replace variables
old, new, old-func and new-func by declared variables.

(math-rwcomp-assoc-args, math-rwcomp-addsub-args):  Remove unnecessary
variable.

(math-rewrite-phase): Declare it.

(math-apply-rw-regs): New variable.
(math-apply-rewrites, math-rwapply-replace-regs,
math-rwapply-reg-looks-negp): Replace variable regs by declared variable.

(math-apply-rw-ruleset): New variable.
(math-apply-rewrites, math-rwapply-remember): Replace variable ruleset
by declared variable.