fact: Fixpoint ps_lap_in α {R : ring α} {K : field R} a l := match l with | [] => False | [b … m] => (l ≠ [])%pslap ∧ (b = a)%ps ∨ ps_lap_in a m end.
imports: Utf8 QArith NPeano Misc Field2 Fpolynomial Puiseux_series Ps_add Ps_mul Ps_div