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

theorem Th39:
  i-'i1>=1 or i-i1>=1 implies i-'i1=i-i1
proof
  assume
A1: i-'i1>=1 or i-i1>=1;
  per cases by A1;
  suppose i-'i1>=1;
    hence thesis by XREAL_0:def 2;
  end;
  suppose i-i1>=1;
    hence thesis by XREAL_0:def 2;
  end;
end;
