theorem Th22:
  a/W + b/W = (a+b)/W & r*(a/W) = (r*a)/W
proof
  thus a/W + b/W = a.W + b.W .= (a+b)/W by Th17;
  thus r*(a/W) = (LMULT W).(r,a.W) by VECTSP_1:def 12
    .= r*(a.W qua Element of V.W) by Def21
    .= (r*a)/W by Def20;
end;
