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• Std/io
• Princ$

Std/io/princ$

Print an atom to a :character output stream.

ACL2 has nice documentation for princ$. The std/io library adds the following lemmas:

Definitions and Theorems

Theorem: state-p1-of-princ$

(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: open-output-channel-p1-of-princ$

(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))))