This axiom is sometimes called the zeroth axiom of set theory (see [[Thermodynamics|Zeroth Law of Thermodynamics]]) because it states something so obvious that it's easy to forget to formally state it as a rule. | This axiom is sometimes called the zeroth axiom of set theory (see [[Thermodynamics|Zeroth Law of Thermodynamics]]) because it states something so obvious that it's easy to forget to formally state it as a rule. |