“…Within this context of bipolarity, bipolar fuzzy relational equations were introduced in [20] as a generalization of fuzzy relational equations [30,31] (one of the core research topics in fuzzy set theory [15,18]), where the unknown variables and their negations appear simultaneously. Most, if not all, publications on bipolar fuzzy relational equations are restricted to the real unit interval [20,26,27,33], as was the case for fuzzy relational equations in the early days. Moreover, the equations considered in the literature are all of the type max- * , with * a triangular norm (t-norm, for short).…”