POSITION-EQ
position of an item in a string or a list, using eq as test
Major Section: PROGRAMMING
(Position-eq item seq) is the least index (zero-based) of the
element item in the list seq, if in fact item is
an element of seq. Otherwise (position-eq item seq) is nil.
(Position-eq item lst) is provably the same in the ACL2 logic as
(position item lst) and (position-equal item lst) when lst is a
true list, but it has a stronger guard because it uses eq for a
more efficient test for whether item is equal to a given member of
lst. Its guard requires that lst is a true list, and moreover,
either item is a symbol or lst is a list of symbols.
See position-equal and see position, which unlike position-eq have
guards that allow the second argument to be a string.
