@article{BovaChenValeriote12,
 author = {Simone Bova and
Hubie Chen and
Matthew Valeriote},
 journal = {Theory Comput. Syst.},
 number = {2},
 pages = {329--353},
 title = {On the Expression Complexity of Equivalence and Isomorphism of Primitive
Positive Formulas},
 volume = {50},
 year = {2012}
}