English
For all R with EuclideanDomain, xgcdAux piecewise definition: xgcdAux(r,s,t,r',s',t') equals (r',s',t') if r = 0, otherwise xgcdAux(r' mod r, s' - (r'/r) s, t' - (r'/r) t, r, s, t).
Русский
Для евклидового кольца: xgcdAux(r,s,t,r',s',t') равно (r',s',t') если r = 0, иначе xgcdAux(r' mod r, s' - (r'/r) s, t' - (r'/r) t, r, s, t).
LaTeX
$$$$ xgcdAux(r,s,t,r',s',t') = \\begin{cases} (r',s',t'), & r=0 \\\\ xgcdAux(r' \\bmod r,\\; s' - (r'/r) s,\\; t' - (r'/r) t,\\; r,s,t), & r \\neq 0 \\end{cases} $$$$
Lean4
theorem div_add_mod' (m k : R) : m / k * k + m % k = m :=
by
rw [mul_comm]
exact div_add_mod _ _