Open immersions #
A morphism is an open immersion if the underlying map of spaces is an open embedding
f : X ⟶ U ⊆ Y, and the sheaf map
Y(V) ⟶ f _* X(V) is an iso for each
V ⊆ U.
Most of the theories are developed in
AlgebraicGeometry/OpenImmersion, and we provide the
remaining theorems analogous to other lemmas in