 reserve n,s for Nat;

theorem Th44:
  n <= Triangle n
  proof
    defpred P[Nat] means $1 <= Triangle $1;
A1: P[0];
A2: for k being Nat st P[k] holds P[k+1]
    proof
      let k be Nat;
      assume P[k];
      Triangle (k + 1) = Triangle (k) + (k + 1) by Th10;
      hence thesis by NAT_1:11;
    end;
    for n being Nat holds P[n] from NAT_1:sch 2(A1,A2);
    hence thesis;
  end;
