 reserve x for Real,
    p,k,l,m,n,s,h,i,j,k1,t,t1 for Nat,
    X for Subset of REAL;

theorem Th2:
  for i being natural Number holds 0 <= i
proof
  let i be natural Number;
A0: i is Nat by TARSKI:1;
  defpred P[natural Number] means 0 <= $1;
A1: for n st P[n] holds P[n+1];
A2: P[0];
  for k holds P[k] from NatInd(A2,A1);
  hence thesis by A0;
end;
