exact c1
case pos.a.left
v u x : VarName
phi : Formula
phi_ih : ∀ (binders : Finset VarName), Rec.fastAdmitsAux v u binders phi → IsSub phi v u (Rec.fastReplaceFree v u phi)
binders : Finset VarName
h1 : Rec.fastAdmitsAux v u (binders ∪ {x}) phi
c1 : ¬v = x
c2 : isFreeIn v phi
⊢ ¬v = x
no goals