Local Notation term := GRing.term.Local Notation True := GRing.True.Local Notation And := GRing.And (only parsing).
Local Notation morphAnd f := ((big_morphf) true andb).
Local Notation eval := GRing.eval.

case: (IHm W) => // [|V simV sVW]; first exact: leq_trans ltWU _. by exists V; last apply: submx_trans sVW sWU.