reserve n for Nat;

theorem
for R being domRing,
    p,q being non zero Polynomial of R
holds card BRoots(p*'q) = card BRoots p + card BRoots q
proof
let R be domRing, p,q be non zero Polynomial of R;
thus card BRoots(p*'q)
   = card(BRoots p + BRoots q) by UPROOTS:56
  .= card BRoots p + card BRoots q by UPROOTS:15;
end;
