  Motivated by the enhanced gauge symmetry phenomenon of the physics literature
and mirror symmetry, this paper constructs an action of an Artin group on the
derived category of coherent sheaves of a smooth quasiprojective threefold
containing a configuration of ruled surfaces described by a finite type Dynkin
diagram. The action extends over deformations of the threefold via a compatible
action of the corresponding reflection group on the base of its deformation
space. All finite type Dynkin diagrams are realized.

Algebraic Geometry