English
If s and t are preconnected in their spaces, then their product s × t is preconnected in the product space.
Русский
Если s и t предсвязаны в своих пространствах, то их произведение s × t предсвязано в произведенном пространстве.
LaTeX
$$$\\mathrm{IsPreconnected}(s) \\land \\mathrm{IsPreconnected}(t) \\Rightarrow \\mathrm{IsPreconnected}(s \\times t)$$$
Lean4
theorem subset_right_of_subset_union (hu : IsOpen u) (hv : IsOpen v) (huv : Disjoint u v) (hsuv : s ⊆ u ∪ v)
(hsv : (s ∩ v).Nonempty) (hs : IsPreconnected s) : s ⊆ v :=
hs.subset_left_of_subset_union hv hu huv.symm (union_comm u v ▸ hsuv) hsv