reserve T for BinContinuous unital TopSpace-like non empty TopGrStr,
  x,y for Point of I[01],
  s,t for unital Point of T,
  f,g for Loop of t,
  c for constant Loop of t;

theorem Th12:
  LoopMlt(f,g),LoopMlt(f+c,c+g) are_homotopic
  proof
    f,f+c are_homotopic & c+g,g are_homotopic by BORSUK_6:80,82;
    hence thesis by Th9;
  end;
