2019/05/20 by Martin-Pizarro, Amador, Ziegler, Martin
#03C45 #FOS: Mathematics #Logic (math.LO)
paper · doi:10.48550/arxiv.1905.08294
A first-order theory is equational if every definable set is a Boolean combination of instances of equations, that is, of formulae such that the family of finite intersections of instances has the descending chain condition. Equationality is a strengthening of stability yet so far only two examples of non-equational stable theories are known. We construct non-equational ω-stable theories by a suitable colouring of the free pseudospace, based on Hrushovski and Srour's original example.