An algebraic proof of the dichotomy for graph orientation problems with forbidden tournaments

For a set F of finite tournaments, the F-free orientation problem is the problem of orienting a given finite undirected graph in such a way that the resulting oriented graph does not contain any member of F. Using the theory of smooth approximations, we give a new shorter proof of the complexity dichotomy for such problems obtained recently by Bodirsky and Guzm\'{a}n-Pro. In fact, our approach yields a complexity dichotomy for a considerably larger class of computational problems where one is given an undirected graph along with additional local constraints on the allowed orientations. Moreover, the border between tractable and hard problems is described by a decidable algebraic condition.