fact: Definition lift_pred m n (f : 'I_n -> 'I_m) : 'I_n.+1 -> 'I_m.+1 := fun (x : 'I_(1 + n)) => if split x is inr j then lift 0 (f j) else 0.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path ssralg) mathcomp(fintype perm choice finfun matrix bigop zmodp poly mxpoly)