reserve x, X, Y for set;
reserve L for complete LATTICE,
  a for Element of L;

theorem Th28: ::Proposition 2.2 (i)  (variant 3)
  for L being non empty RelStr holds (for A being Subset of L
  holds ex_inf_of A,L) implies L is complete
proof
  let L be non empty RelStr;
  assume for A being Subset of L holds ex_inf_of A,L;
  then for X holds ex_inf_of X, L by Th26;
  hence thesis by Th25;
end;
