 Similarly, as usual in category theory, given two spaces that are homeomorphic, the space of homeomorphisms between them, formula_36 is a torsor for the homeomorphism groups formula_35 and formula_38, and, given a specific homeomorphism between formula_6 and formula_7, all three sets are identified.The intuitive criterion of stretching, bending, cutting and gluing back together takes a certain amount of practice to apply correctly—it may not be obvious from the description above that deforming a line segment to a point is impermissible, for instance.It is thus important to realize that it is the formal definition given above that counts.