Remark ReplaceTermTermsTermIsPR : isPR 2 ReplaceTermTermsTerm.
Definition ReplaceTermTerm (t s : nat) : nat :=
cPairPi1 (ReplaceTermTermsTerm t s).
Definition ReplaceTermsTerm (t s : nat) : nat :=
cPairPi2 (ReplaceTermTermsTerm t s).

Lemma ReplaceTermTermMonotone :
forall a s1 s2 : nat,
s1 <= s2 -> ReplaceTermTerm a s1 <= ReplaceTermTerm a s2.