Print an atom to a
ACL2 has nice documentation for princ$. The std/io library adds the following lemmas:
Theorem:
(defthm state-p1-of-princ$ (implies (and (state-p1 state) (symbolp channel) (open-output-channel-p1 channel :character state)) (state-p1 (princ$ x channel state))))
Theorem:
(defthm open-output-channel-p1-of-princ$ (implies (and (state-p1 state) (open-output-channel-p1 channel :character state)) (open-output-channel-p1 channel :character (princ$ x channel state))))