English
The image of the left coordinate under the segment mapping equals the segment between (x1,y) and (x2,y).
Русский
Образ левого координатного компонента под отображением сегмента равен сегменту между (x1,y) и (x2,y).
LaTeX
$$$ (\lambda x).(x,y) '' [x_{1} -[\mathbb{k}] x_{2}] = [ (x_{1},y) -[\mathbb{k}] (x_{2},y) ] $$$
Lean4
theorem image_mk_segment_left (x₁ x₂ : E) (y : F) : (fun x => (x, y)) '' [x₁ -[𝕜] x₂] = [(x₁, y) -[𝕜] (x₂, y)] :=
by
rw [segment_eq_image₂, segment_eq_image₂, image_image]
refine EqOn.image_eq fun a ha ↦ ?_
simp [Convex.combo_self ha.2.2]