Definition Formula := Formula LNT.
Definition Formulas := Formulas LNT.
Definition System := System LNT.
Definition Sentence := Sentence LNT.
Definition Term := Term LNT.
Definition Terms := Terms LNT.
Definition var := var LNT.
Definition equal := equal LNT.
Definition impH := impH LNT.
Definition notH := notH LNT.
Definition iffH := iffH LNT.
Definition forallH := forallH LNT.
Definition orH := orH LNT.
Definition andH := andH LNT.
Definition existH := existH LNT.
Definition ifThenElseH := ifThenElseH LNT.
Definition SysPrf := SysPrf LNT.
Definition Plus (x y : Term) : Term :=
apply LNT Plus (Tcons LNT 1 x (Tcons LNT 0 y (Tnil LNT))).
Definition Times (x y : Term) : Term :=
apply LNT Times (Tcons LNT 1 x (Tcons LNT 0 y (Tnil LNT))).
Definition Succ (x : Term) : Term :=
apply LNT Succ (Tcons LNT 0 x (Tnil LNT)).
Definition Zero : Term := apply LNT Zero (Tnil LNT).

Lemma freeVarPlus :
forall x y : Term,
freeVarTerm LNT (Plus x y) = freeVarTerm LNT x ++ freeVarTerm LNT y.