split_ifs
z : String
t : Var
x : String
⊢ (if free_ z = free_ x then t else free_ x).freeVarSet ⊆ t.freeVarSet ∪ (free_ x).freeVarSet \ {free_ z}
case pos
z : String
t : Var
x : String
h✝ : free_ z = free_ x
⊢ t.freeVarSet ⊆ t.freeVarSet ∪ (free_ x).freeVarSet \ {free_ z}

case neg
z : String
t : Var
x : String
h✝ : ¬free_ z = free_ x
⊢ (free_ x).freeVarSet ⊆ t.freeVarSet ∪ (free_ x).freeVarSet \ {free_ z}