Generic Expression Hardness Results for Primitive Positive Formula   Comparison
  We study the expression complexity of two basic problems involving the comparison of primitive positive formulas: equivalence and containment. In particular, we study the complexity of these problems relative to finite relational structures. We present two generic hardness results for the studied problems, and discuss evidence that they are optimal and yield, for each of the problems, a complexity trichotomy. 
Simone Bova and Hubie Chen and Matthew Valeriote
cs.LO cs.CC cs.DB