English
For any v in the direction of s, s.SSameSide (v +ᵥ x) y iff s.SSameSide x y.
Русский
Для любого v в направлении s: s.SSameSide (v +ᵥ x) y ⇔ s.SSameSide x y.
LaTeX
$$$\forall s: \text{AffineSubspace}(R,P)\ \forall x,y: P\;\forall v\in s.direction,\; s.SSameSide( v +ᵥ x) y \iff s.SSameSide x y$$$
Lean4
theorem sSameSide_vadd_left_iff {s : AffineSubspace R P} {x y : P} {v : V} (hv : v ∈ s.direction) :
s.SSameSide (v +ᵥ x) y ↔ s.SSameSide x y := by
rw [SSameSide, SSameSide, wSameSide_vadd_left_iff hv, vadd_mem_iff_mem_of_mem_direction hv]