Let be a smooth connected ample curve in an abelian surface . Translate its chosen basepoint to zero and apply the universal property of the Jacobian variety. The image of is a closed connected algebraic subgroup containing the translated curve. If it had dimension one, that curve would be the subgroup itself; a distinct coset is disjoint and numerically equivalent, forcing . This contradicts ampleness, so the homomorphism is surjective.
Choose a projective embedding of the abelian surface . By Bertini's theorem, a general hyperplane section is a smooth projective curve that is connected. It is ample, so . Choose and translate the inclusion so it sends to the identity of . The universal property of the Jacobian variety then gives a homomorphism of abelian varieties
whose composition with the based Abel map of an algebraic curve is this translated inclusion.
The image is a closed connected algebraic subgroup, since is projective, and it contains a translate of . If the image had dimension one, that irreducible curve would be the image subgroup itself. A distinct coset is disjoint from it and has the same numerical divisor class: translation acts trivially on cohomology, being homotopic to the identity on the complex torus. Its self-intersection would therefore be zero, contradicting . The image has dimension two and is all of . Thus is surjective, as expressed by the principle that an ample curve on an abelian surface generates the surface.
A minimal algebraic surface is a smooth projective surface containing no exceptional curve of the first kind, namely no smooth rational curve of self-intersection . An abelian surface contains no rational curve because every morphism from to an abelian variety is constant. It therefore has no -curve and is minimal.
For every , the Minimal Hirzebruch surface is a rational minimal surface. These surfaces are pairwise nonisomorphic: the negative section is the unique irreducible curve of negative self-intersection and has square , so an isomorphism would recover . Thus there are infinitely many nonisomorphic minimal rational surfaces.
A K3 surface is a smooth projective surface with and . For a smooth curve of geometric genus , the adjunction formula gives
and hence
An elliptic surface is a smooth projective surface with a morphism to a smooth curve whose generic fiber is a smooth genus-one curve. If is an elliptic curve, projection
is an elliptic fibration. Its canonical bundle is pulled back from , so every positive pluricanonical space vanishes and the Kodaira dimension is . This supplies the requested negative-Kodaira-dimension example.
For an elliptically fibered K3 surface, choose a smooth quartic containing a line . The canonical bundle of a smooth projective hypersurface formula makes trivial, and the standard cohomology sequence gives , so is K3. The pencil of planes through cuts into plus a residual plane cubic. The residual linear system is basepoint-free, has square zero and defines a morphism whose generic fiber is a smooth plane cubic. This is the Elliptic K3 surface from a quartic containing a line.
A surface of general type is a smooth projective surface of Kodaira dimension two. Let be a smooth plane curve of degree eight and let
be the degree-two cover branched along . The branch-cover canonical-bundle formula gives
This divisor is ample, so is a double plane of general type and is the required finite morphism of degree two.