Recognizer for when a given list of terms calls only
:logic-mode function symbols
For a list x of terms in worldwrld,
(logic-fns-listp x wrld) is true if and only if every function symbol
called in x is in :logic mode in wrld. Unlike logic-term-listp, logic-fns-listp does not check that x is a list
of terms; rather, logic-fns-listp should only be applied to such lists.
See defun-mode-lambdas for some clarifications of how :program
mode functions are allowed in certain :logic mode terms.