English
Equality of dlookup on kunion with a not in the first keys implies equality with the second side.
Русский
Эквивалентность dlookup на kunion, если a не в ключах, равна dlookup на второй списке.
LaTeX
$$$ a \\notin l_1.\\keys \\Rightarrow dlookup(a,kunion(l_1,l_2)) = dlookup(a,l_2) $$$
Lean4
nonrec theorem cons {r : α → α → Prop} [IsTrans α r] {l : List α} {a b : α} (hab : r a b) (h : Sorted r (b :: l)) :
Sorted r (a :: b :: l) :=
h.cons <| forall_mem_cons.2 ⟨hab, fun _ hx => _root_.trans hab <| rel_of_sorted_cons h _ hx⟩