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

theorem :: NAT_D:43
  m-n >= 0 implies m-'n+n = m
  proof
    assume m-n >= 0;
    then m-'n = m-n by XREAL_0:def 2;
    hence thesis;
  end;
