fact: Definition parser (x : pos_neg_int63) : option int := match x with | Pos p => if (p <? 4611686018427387904)%uint63 then Some p else None | Neg n => if (n <=? 4611686018427387904)%uint63 then Some ((n - 1) lxor max_int)%uint63 else None end.
imports: ZArith Uint63 Lia