@article{simon11two, author = {A. Simon and A. King and J. Howe}, title = {The {T}wo {V}ariable {P}er {I}nequality {A}bstract {D}omain}, journal = {Higher Order and Symbolic Computation}, year = 2011, publisher = {Springer}, doi = {10.1007/s10990-010-9062-8}, }