David N. Yetter

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The purpose of this note is to announce a new isotopy invariant of oriented links of tamely embedded circles in 3-space. We represent links by plane projections, using the customary conventions that the image of the link is a union of transversely intersecting immersed curves, each provided with an orientation, and undercrossings are indicated by broken(More)
Using the theory of measurable categories developped in [Yet03], we provide a notion of representations of 2-groups more well-suited to physically and geometrically interesting examples than that using 2-VECT (cf. [KV94]). Using this theory we sketch a 2-categorical approach to the state-sum model for Lorentzian quantum gravity proposed in [CY03], and(More)
The 2-category of all small categories equivalent to a (finite) cartesian product of the category of finite dimensional vector spaces over a fixed field, left-exact functors, and natural transformations has structures closely mimicking those found in ordinary linear algebra. We examine these structures, the relation of this category to the 2-categories and(More)
This paper summarizes substantive new results derived by a student team (the first three authors) under the direction of the fourth author at the 2005 session of the KSU REU " Brainstorming and Barnstorming ". The main results are a decomposition theorem for quandles in terms of an operation of 'semidisjoint union' showing that all finite quandles(More)