
theorem  :: Proposition 2 6L
  for R being non empty RelStr,
      X, Y being Subset of R st
    X c= Y holds LAp X c= LAp Y
  proof
    let R be non empty RelStr;
    let X, Y be Subset of R;
    assume
A1: X c= Y;
    let y be object;
    assume y in LAp X; then
    consider z being Element of R such that
A2: z = y & Class (the InternalRel of R, z) c= X;
    Class (the InternalRel of R, z) c= Y by A1,A2;
    hence thesis by A2;
  end;
