Proceedings of Symbolic Computation Conferences summer 2007 : proceedings of the 2007 ACM International Symposium on Symbolic and Algebraic Computation (ISSAC 2007) : proceedings of the 2007 International Workshop on Parallel Symbolic Computation (PASCO 2007) : proceedings of the 2007 International Workshop on Symbolic-Numeric Computation (SNC 2007) (Association for Computing Machinery, 2007)