case _ c1 =>
  rfl
D : Type
I : Interpretation D
V : VarAssignment D
F : Formula
z : String
h1 : ¬occursFreeIn (free_ z) F
d : D
x' : String
a1 : occursFreeIn (free_ x') F
c1 : ¬free_ x' = free_ z
⊢ V (free_ x') = V (free_ x')
no goals