reserve V for RealLinearSpace,
  u,u1,u2,v,v1,v2,w,w1,x,y for VECTOR of V,
  a,a1,a2,b,b1,b2,c1,c2,n,k1,k2 for Real;

theorem
  Gen x,y implies Ortm(x,y,0.V) = 0.V
proof
  assume
A1: Gen x,y;
  set u = the VECTOR of V;
  thus Ortm(x,y,0.V) = Ortm(x,y,0*u) by RLVECT_1:10
    .= 0*Ortm(x,y,u) by A1,Th2
    .= 0.V by RLVECT_1:10;
end;
