English
For every u in XgcdType, the v-coordinate is unchanged by reduction: (u.reduce).v = u.v.
Русский
Для всякого u из XgcdType координата v сохраняется при редукции: (u.reduce).v = u.v.
LaTeX
$$$\forall u : XgcdType, (u.reduce).v = u.v$$$
Lean4
theorem reduce_v : ∀ u : XgcdType, u.reduce.v = u.v
| u =>
dite (u.r = 0) (fun h => by rw [reduce_a h, finish_v u h]) fun h =>
by
have : SizeOf.sizeOf u.step < SizeOf.sizeOf u := u.step_wf h
rw [reduce_b h, flip_v, reduce_v (step u), step_v u h, Prod.swap_swap]