(multiple-value-list (xgcd 77874422 32223899))
(1 23017069 -55624583)

(let ((a 974507656412513757857315037382926980395082974811562770185617915360)
      (b -1539496810360685510909469177732386446833404488164283))
  (multiple-value-bind (g u v) (xgcd a b)
    (and (eql g 1) (eql g (+ (* a u) (* b v))))
) )
T