When applied to a pair of terms (u,x), where x is just a variable,
and a goal A ?- t, the tactic SPEC_TAC generalizes the goal to
A ?- !x. t[x/u], that is, all instances of u are turned into x.
A ?- t
================= SPEC_TAC (u,x)
A ?- !x. t[x/u]
FAILURE
Fails unless x is a variable with the same type as u.
USES
Removing unnecessary speciality in a goal, particularly as a prelude to
an inductive proof.