Let codeFormula := codeFormula LNN codeLNTFunction codeLNNRelation.

Lemma FixPointLNN :
forall (A : Formula) (v : nat),
{B : Formula |
SysPrf NN
(iffH B (substituteFormula LNN A v (natToTermLNN (codeFormula B)))) /\
(forall x : nat,
In x (freeVarFormula LNN B) <->
In x (list_remove _ eq_nat_dec v (freeVarFormula LNN A)))}.