Roberto Passerone Jerry R. Burch Alberto L. Sangiovanni-Vincentelli Refinement preserving approximations for the design and verification of heterogeneous systems. 1-33 2007 31 Formal Methods in System Design 1 http://dx.doi.org/10.1007/s10703-006-0024-z db/journals/fmsd/fmsd31.html#PasseroneBS07