 One immediate worry about the left-to-right direction of  Indiscernibility  is that according to standard set theory there are no functions whose domain and range include all objects (assuming sets count as  “objects”).[23]  There are various possible ways around this problem. For example, one might replace the quantifier over “functions” with a plural quantifier over ordered pairs, or a higher-order quantifier binding a variable in dyadic predicate  position.[24] 