reserve n,m,k for Nat;
reserve r,r1 for Real;
reserve f,seq,seq1 for Real_Sequence;
reserve x,y for set;
reserve e1,e2 for ExtReal;

theorem Th6:
  seq is non-decreasing iff for n,m st n<=m holds seq.n<=seq.m
proof
  thus seq is non-decreasing implies for n,m st n<=m holds seq.n<=seq.m
  proof
    assume seq is non-decreasing;
    then for n,k holds seq.n<=seq.(n+k) by Th5;
    hence thesis by Lm4;
  end;
  assume
A1: for n,m st n<=m holds seq.n<=seq.m;
  let n,m;
  assume that
  n in dom seq and
  m in dom seq and
A2: n <= m;
  thus thesis by A1,A2;
end;
