We only provide a higher-level description of the method; for a complete derivation and the theory justifying the algorithm we refer the reader to the works by Hsu et al.
to Equation 2, which uses the longest context x of length n to compute the conditional probability, the interpolated model leverages the ability of the PNFA to model substring expectations of all lengths up to n. This is similar to classic interpolation of language models (Rosenfeld, 1994;Chen, 2009).