 reserve x for Real,
    p,k,l,m,n,s,h,i,j,k1,t,t1 for Nat,
    X for Subset of REAL;
reserve x for object, X,Y,Z for set;
 reserve M,N for Cardinal;

theorem
  for n being natural Number holds n in Segm(n+1)
proof
  let n be natural Number;
A1: n is Nat by TARSKI:1;
  n<n+1 by XREAL_1:29;
  then n in {l where l is Nat:l<n+1} by A1;
  hence thesis by AXIOMS:4;
