Which of the following statement is not correct?
1
The union of any two subgroups of a group G is also a subgroup of G.
2
The intersection of any two subgroups of a group G is also subgroup of G.
3
The union of two subgroups H1 and H2 of a group (G, * ) is also subgroup of G.
4
Every subgroup of an abelian group is also an abelian group.