English
The sum of a general vector v with a vecCons y w equals vecCons (head v + y) (tail v + w).
Русский
Сумма произвольного вектора v и vecCons y w равна vecCons (head v + y) (tail v + w).
LaTeX
$$$ v + \mathrm{vecCons} y w = \mathrm{vecCons}(\mathrm{vecHead} v + y) (\mathrm{vecTail} v + w) $$$
Lean4
@[simp]
theorem add_cons (v : Fin n.succ → α) (y : α) (w : Fin n → α) :
v + vecCons y w = vecCons (vecHead v + y) (vecTail v + w) := by ext i;
refine i.cases ?_ ?_ <;> simp [vecHead, vecTail]