∀ {α : Type u_1} {r : α → α → Prop} [inst : DecidableRel r] [Std.Total r] [IsTrans α r] {l l' : List α},
  List.Pairwise r l → List.Pairwise r l' → List.Pairwise r (l.merge l' fun x1 x2 => decide (r x1 x2))