reserve a,b,p,k,l,m,n,s,h,i,j,t,i1,i2 for natural Number;

theorem
  j + k <= i implies k <= i -' j
proof
  assume
A1: j + k <= i;
  per cases by A1,XXREAL_0:1;
  suppose j + k = i;
    hence thesis by Th34;
  end;
  suppose j + k < i;
    hence thesis by Th52;
  end;
end;
