theorem Th38:
  for H2,H3 being strict StableSubgroup of G holds H1 is
  StableSubgroup of H2 implies H1 "\/" H3 is StableSubgroup of H2 "\/" H3
proof
  let H2,H3 be strict StableSubgroup of G;
  assume H1 is StableSubgroup of H2;
  then H1 is Subgroup of H2 by Def7;
  then carr H1 c= carr H2 by GROUP_2:def 5;
  hence thesis by Th26,XBOOLE_1:9;
end;
