In particular, the set of all counterexamples contains a minimal element, the "minimal counterexample". Weak rule utilitarianism (WRU) attempts to handle SRU counterexamples as legitimate exceptions. There are no known counterexamples to the conjecture. Equivalence relations are a ready source of examples or counterexamples. Putative counterexamples to the law of excluded middle include the liar paradox or Quine's paradox. Heyting algebras can supply all the counterexamples to non-laws of Heyting algebra. However, none of these known counterexamples is bipartite. Weak counterexamples of this sort are often related to the limited principle of omniscience. There are closed quotients of the Moore plane that provide counterexamples. Therefore, it serves as one of the basic counterexamples of topology. There are similar counterexamples for more than two random variables. It is an example of pathological function which provides counterexamples to many situations. Brouwer also provided "weak" counterexamples. Michael Otsuka provides a more specific answer to proposed problems with Frankfurt's counterexamples. For counterexamples, see Gateaux derivative.