cases l
x : ℕ
ψ φ1 : Formula
l : List Formula
⊢ repl_in_F x ψ (dis (φ1 :: l)) = dis (List.map (repl_in_F x ψ) (φ1 :: l))
case nil
x : ℕ
ψ φ1 : Formula
⊢ repl_in_F x ψ (dis [φ1]) = dis (List.map (repl_in_F x ψ) [φ1])

case cons
x : ℕ
ψ φ1 head✝ : Formula
tail✝ : List Formula
⊢ repl_in_F x ψ (dis (φ1 :: head✝ :: tail✝)) = dis (List.map (repl_in_F x ψ) (φ1 :: head✝ :: tail✝))