Subgroup of double coset index two

Definition
A subgroup is said to have double coset index two if its double coset index is exactly two.

Stronger properties

 * Weaker than::Subgroup of index two
 * Non-normal subgroup of index three:
 * Subgroup of index four that is not 2-subnormal:

Weaker properties

 * Stronger than::Double coset-separated subgroup
 * Stronger than::Double coset-ordering subgroup
 * Stronger than::Maximal subgroup:
 * Stronger than::1-completed subgroup
 * Stronger than::Subgroup of finite double coset index
 * Stronger than::Elliptic subgroup