theorem
  x<>0.F implies x"*(x*v)=v
proof
  assume
A1: x<>0.F;
  x"*(x*v) = (x"*x)*v by VECTSP_1:def 16
    .= 1_F *v by A1,Th9
    .= v by VECTSP_1:def 17;
  hence thesis;
end;
