simp at c1
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') = d
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 : x' = z
⊢ V (free_ x') = d