]> 2010-03-15T23:02:17-07:00 Union of two subgroups is not a subgroup unless they are comparable Fact 48 Exercise 8 states only the particular case of proving that the union is a subgroup iff one is contained in the other 48 Exercise 8 states only the particular case of proving that the union is a subgroup iff one is contained in the other Stated in Book:DummitFoote Referenced in Page class Elementary non-basic facts in group theory