English
For any R and sets s1, s2, the image of their union equals the union of their images: image R (s1 ∪ s2) = image R s1 ∪ image R s2.
Русский
Образ объединения равен объединению образов: image R (s1 ∪ s2) = image R s1 ∪ image R s2.
LaTeX
$$$\\forall (R : SetRel \\alpha \\beta) (s1 s2 : Set \\alpha),\\\\ image\\,R\\,(s1 \\cup s2) = image\\,R\\,s1 \\cup image\\,R\\,s2$$$
Lean4
theorem image_union : image R (s₁ ∪ s₂) = image R s₁ ∪ image R s₂ := by aesop