
theorem Th20:
  for L be non empty RelStr holds [#]L is infs-closed sups-closed
proof
  let L be non empty RelStr;
  for X be Subset of [#]L st ex_inf_of X,L holds "/\"(X,L) in [#]L;
  hence [#]L is infs-closed by WAYBEL23:19;
  for X be Subset of [#]L st ex_sup_of X,L holds "\/"(X,L) in [#]L;
  hence thesis by WAYBEL23:20;
end;
