reserve x,y,z,X for set,
  T for Universe;

theorem Th11:
  for S being 1-sorted, N being NetStr over S, M be SubNetStr of N
  , x,y being Element of N, i,j being Element of M st x = i & y = j & i <= j
  holds x <= y
proof
  let S be 1-sorted, N be NetStr over S, M be SubNetStr of N, x,y be Element
  of N, i,j be Element of M such that
A1: x = i & y = j and
A2: i <= j;
  reconsider M as SubRelStr of N by Def6;
  reconsider i9 = i, j9 = j as Element of M;
  i9 <= j9 by A2;
  hence thesis by A1,YELLOW_0:59;
end;
