 Inverse image functor

In mathematics, specifically in algebraic topology and algebraic geometry, an inverse image functor is a contravariant construction of sheaves; here “contravariant” in the sense given a map formula_1, the inverse image functor is a functor from the category of sheaves on "Y" to the category of sheaves on "X".The direct image functor is the primary operation on sheaves, with the simplest definition.