Crosscap slides and the level 2 mapping class group of a nonorientable surface

Crosscap slide is a homeomorphism of a nonorientable surface of genus at least 2, which was introduced under the name Y-homeomorphism by Lickorish as an example of an element of the mapping class group which cannot be expressed as a product of Dehn twists. We prove that the subgroup of the mapping class group of a closed nonorientable surface N generated by all crosscap slides is equal to the level 2 subgroup consisting of those mapping classes which act trivially on ${H_1(N;\mathbb{Z}_2)}$ . We also prove that this subgroup is generated by involutions.