A useful set of 4v-s-expression rewrite rules, proven correct.
Theorem:
(defthm nth-4v-sexpr-eval-list (equal (nth n (4v-sexpr-eval-list x env)) (if (< (nfix n) (len x)) (4v-sexpr-eval (nth n x) env) nil)))
Theorem:
(defthm 4v-sexpr-rewritesp-sexpr-rewrites (4v-sexpr-rewrite-alistp *sexpr-rewrites*))