Omid Amini Fedor V. Fomin Saket Saurabh Counting Subgraphs via Homomorphisms. 71-82 2009 ICALP (1) http://dx.doi.org/10.1007/978-3-642-02927-1_8 conf/icalp/2009-1 db/conf/icalp/icalp2009-1.html#AminiFS09