e/Difference hierarchy

Information
has gloss	eng: In set theory, the difference hierarchy over a pointclass is a hierarchy of larger pointclasses generated by taking differences of sets. If Γ is a pointclass, then the set of differences in Γ is \A:\exists C,D\in\Gamma ( A = C\setminus D)\}. In usual notation, this set is denoted by 2-Γ. The next level of the hierarchy is denoted by 3-Γ and consists of differences of three sets: \A : \exists C,D,E\in\Gamma ( A=C\setminus(D\setminus E))\}. This definition can be extended recursively into the transfinite to α-Γ for some ordinal α.
lexicalization	eng: Difference hierarchy
instance of	c/Mathematical logic hierarchies