 reserve V for Z_Module;
 reserve W for Subspace of V;
 reserve v, u for Vector of V;
 reserve i for Element of INT.Ring;

theorem
  for X, Y be free Z_Module, T be linear-transformation of X, Y
  st T is bijective holds
  X is finite-rank iff Y is finite-rank
  proof
    let X, Y be free Z_Module,
    T be linear-transformation of X, Y;
    assume AS1: T is bijective;
    consider K be linear-transformation of Y, X such that
    AS3: K= T" & K is bijective by HM1,AS1;
    thus thesis by HM13,AS1,AS3;
  end;
