have := Clause.of_maxLiteral_eq_none clause (List.all_none_of_filterMap_eq_nil h clause hclause1) lit
case intro.intro
c : CNF Nat
lit : Nat
h : List.filterMap Clause.maxLiteral c = []
clause : Clause Nat
hclause1 : clause ∈ c
hclause2 : Clause.mem lit clause
⊢ False
case intro.intro
c : CNF Nat
lit : Nat
h : List.filterMap Clause.maxLiteral c = []
clause : Clause Nat
hclause1 : clause ∈ c
hclause2 : Clause.mem lit clause
this : ¬Clause.mem lit clause
⊢ False