Injective sheaf
= Injective sheaf
A sheaf of abelian groups is injective if every morphism to it from a subsheaf extends to the containing sheaf. Every such sheaf embeds in an injective sheaf. Injective sheaves are <flasque>: the inclusion of <extension by zero> constant-integer sheaves associated to $U\subseteq V$ turns the extension property into surjectivity of restriction from $V$ to $U$.