reserve S, R for 1-sorted,
  X for Subset of R,
  T for TopStruct,
  x for set;
reserve H for non empty multMagma,
  P, Q, P1, Q1 for Subset of H,
  h for Element of H;
reserve G for Group,
  A, B for Subset of G,
  a for Element of G;

theorem Th50:
  for G being UnContinuous TopGroup, O being open Subset of G holds O" is open
proof
  let G be UnContinuous TopGroup, O be open Subset of G;
  O" = (inverse_op G).:O by Th9;
  hence thesis by Th24;
end;
