intuition.
Qed.
Set Implicit Arguments.
Unset Strict Implicit.
Definition minusTerm : Term -> Term -> Term.
intros H; case H; intros b2 c2 H'; case H'; intros b3 c3;
exact (minusA b2 b3, c2).
Defined.
Set Strict Implicit.
Unset Implicit Arguments.

Theorem eqTerm_minusTerm_plusTerm_invTerm :
forall a b : Term, eqTerm (minusTerm a b) (plusTerm a (invTerm b)).