Deformations of ordered semigroup rings
by
James J. Madden
LSU-Baton Rouge

I give an example of a totally-ordered ring A that is not formally real, but whose monoid of archimedean classes H(A) is a Rees quotient of a submonoid of the natural numbers. This gives a negative solution to a question posed in Evans, et al., Totally ordered commutative monoids, to appear in Semigroup Forum. The example is a deformation of the monoid algebra R(H(A)). In general, the deformations of a monoid algebra are classified by a certain cohomology group, and I will discuss generalizations of the example from this point of view.

Date received: February 7, 2000

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