. exact List.mem_of_elem_eq_true
case mp
n : Nat
c : DefaultClause n
l : Literal (PosFin n)
⊢ List.elem l c.clause = true → l ∈ c.toList

case mpr
n : Nat
c : DefaultClause n
l : Literal (PosFin n)
⊢ l ∈ c.toList → List.elem l c.clause = true
case mpr
n : Nat
c : DefaultClause n
l : Literal (PosFin n)
⊢ l ∈ c.toList → List.elem l c.clause = true