Assume-guarantee contract algebras are bounded Sugihara monoids

In [Incer Romeo, I. X., \textit{The Algebra of Contracts}. Ph.D. Thesis, UC Berkeley (2022)] an algebraic perspective on assume-guarantee contracts is proposed. This proposal relies heavily on a construction involving Boolean algebras. However, the structures thus proposed lack a clearly prescribed set of basic operations, necessary if we want to see them as a class of algebras (in the sense of Universal Algebra). In this article, by prescribing a suitable set of basic operations on contracts, we manage to describe these algebras as (a generating set of members of) well-known varieties.