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

theorem
  for i,j being natural Number holds
  i <= j & j <= i + 1 implies i = j or j = i + 1
proof
  let i,j be natural Number;
  assume that
A1: i <= j and
A2: j <= i + 1;
  j <= i or j = i + 1 by A2,Th8;
  hence thesis by A1,XXREAL_0:1;
end;
