∀ {R : Type u_1} {M : Type u_2} {N : Type u_3} [inst : CommRing R] [inst_1 : PartialOrder R] [inst_2 : IsOrderedRing R]
  [inst_3 : TopologicalSpace R] [inst_4 : ClosedIciTopology R] [inst_5 : AddCommGroup M] [inst_6 : Module R M]
  [inst_7 : TopologicalSpace M] [inst_8 : AddCommGroup N] [inst_9 : Module R N] [inst_10 : TopologicalSpace N]
  {p : M →ₗ[R] N →ₗ[R] R} [inst_11 : p.IsContPerfPair] (s t : Set M),
  ProperCone.dual p (s ∪ t) = ProperCone.dual p s ⊓ ProperCone.dual p t