Turing reduction
Although there are many known types of oracles, the choice of which to use can be simplified, because many of them are equivalent in computational power. An oracle formula_15 is said to be "polynomially reducible" to another oracle formula_16 if any call to formula_15 may be simulated by an algorithm that accesses the matroid using only oracle formula_16 and takes polynomial time as measured in terms of the number of elements of the matroid; in complexity-theoretic terms, this is a Turing reduction. Two oracles are said to be "polynomially equivalent" if they are polynomially reducible to each other. If formula_15 and formula_16 are polynomially equivalent, then every result that proves the existence or nonexistence of a polynomial time algorithm for a matroid problem using oracle formula_15 also proves the same thing for oracle formula_16.