According to the Cobham-Edmonds Thesis the complexity class \(\textbf{P}\) describes the class of feasibily decidable problems. As we have just seen, this class is defined in terms of the reference model \(\mathfrak{T}\) in virtue of the assumption that it is a ‘reasonable’ model of computation. Several other models of computation are also studied in complexity theory not because they are presumed to be accurate representations of the costs of concretely embodied computation, but rather because they help us better understand the limits of feasible computability. The most important of these is the non-deterministic Turing machine model \(\mathfrak{N}\).