AP_TERM_TAC : tactic
Strips a function application from both sides of an equational goal.
reduces a goal of the form
A ?- f x = f y
by stripping away the function applications, giving the new goal
A ?- x = y
A ?- f x = f y ================ AP_TERM_TAC A ?- x = y
Fails unless the goal is equational, with both sides being applications of the same function.