English
The strong opposite-side relation SOppSide is symmetric in x and y for any affine subspace s: s.SOppSide x y iff s.SOppSide y x.
Русский
Строгое отношение SOppSide симметрично по x и y: s.SOppSide x y ⇔ s.SOppSide y x.
LaTeX
$$$\forall s: \text{AffineSubspace}(R,P)\ \forall x,y: P,\; s.SOppSide\; x\; y \iff s.SOppSide\; y\; x$$$
Lean4
theorem sOppSide_comm {s : AffineSubspace R P} {x y : P} : s.SOppSide x y ↔ s.SOppSide y x := by
rw [SOppSide, SOppSide, wOppSide_comm, and_comm (b := x ∉ s)]