reserve i,j,k,m,n for Nat;
reserve R for non empty doubleLoopStr;
reserve x,y for Scalar of R;
reserve f,g,h for FinSequence of R;

theorem
  x is being_a_square & y is being_a_square or x is
  being_a_sum_of_squares & y is being_a_square implies x+y is
  being_a_sum_of_squares by Lm56,Lm62;
