theorem Th2:
  Gen x,y implies Ortm(x,y,n*u)= n*Ortm(x,y,u)
proof
  assume
A1: Gen x,y;
  hence Ortm(x,y,n*u)=n*pr1(x,y,u)*x + (-pr2(x,y,n*u))*y by Lm7
    .=n*pr1(x,y,u)*x + (-(n*pr2(x,y,u)))*y by A1,Lm7
    .=n*pr1(x,y,u)*x + (n*pr2(x,y,u)*(-y)) by RLVECT_1:24
    .=n*pr1(x,y,u)*x + (-(n*pr2(x,y,u)*y)) by RLVECT_1:25
    .=n*pr1(x,y,u)*x + (-(n*(pr2(x,y,u)*y))) by RLVECT_1:def 7
    .=n*pr1(x,y,u)*x + n*(-pr2(x,y,u)*y) by RLVECT_1:25
    .=n*(pr1(x,y,u)*x) + n*(-pr2(x,y,u)*y) by RLVECT_1:def 7
    .=n*((pr1(x,y,u)*x) + (-pr2(x,y,u)*y)) by RLVECT_1:def 5
    .=n*((pr1(x,y,u)*x) + (pr2(x,y,u)*(-y))) by RLVECT_1:25
    .=n*Ortm(x,y,u) by RLVECT_1:24;
end;
