Ingo Feinerer Reinhard Pichler Emanuel Sallinger Vadim Savenkov On the Undecidability of the Equivalence of Second-Order Tuple Generating Dependencies. 2011 AMW http://ceur-ws.org/Vol-749/paper5.pdf conf/amw/2011 db/conf/amw/amw2011.html#FeinererPSS11