theorem Th8:
  (FuncExtMult(X,Y)).[a,(FuncExtMult(X,Y)).[b,f]] = (FuncExtMult(X ,Y)).[a*b,f]
proof
 reconsider a,b as Element of REAL by XREAL_0:def 1;
  now
    let x be Element of X;
    thus ((FuncExtMult(X,Y)).[a,(FuncExtMult(X,Y)).[b,f]]).x = a*(((
    FuncExtMult(X,Y)).[b,f]).x) by Th2
      .= a*(b*(f.x)) by Th2
      .= (a*b)*(f.x) by RLVECT_1:def 7
      .= ((FuncExtMult(X,Y)).[a*b,f]).x by Th2;
  end;
  hence thesis by FUNCT_2:63;
end;
