reserve a,b,i,k,m,n for Nat;
reserve s,z for non zero Nat;
reserve r for Real;
reserve c for Complex;
reserve e1,e2,e3,e4,e5 for ExtReal;

theorem Th2:
  e1 <= e2 <= e3 <= e4 <= e5 implies e1 <= e5
  proof
    assume e1 <= e2 <= e3 <= e4;
    then e1 <= e4 by Th1;
    hence thesis by XXREAL_0:2;
  end;
