Yann Loyer Nicolas Spyratos Daniel Stamate Computing and Comparing Semantics of Programs in Four-Valued Logics. 59-69 1999 conf/mfcs/1999 MFCS db/conf/mfcs/mfcs99.html#LoyerSS99 http://dx.doi.org/10.1007/3-540-48340-3_6