Turing reduction
Let formula_1 be the set of Turing degrees of sets of natural numbers. Given some equivalence class formula_2, we may define the "cone" (or "upward cone") of formula_3 as the set of all Turing degrees formula_4 such that formula_5; that is, the set of Turing degrees that are "at least as complex" as formula_6 under Turing reduction.