OpenFst is a library for constructing, combining, optimizing, and
searching weighted finite-state transducers (FSTs). Weighted
finite-state transducers are automata where each transition has an input
label, an output label, and a weight. The more familiar finite-state
acceptor is represented as a transducer with each transition's input and
output label equal. Finite-state acceptors are used to represent sets of
strings (specifically, regular or rational sets); finite-state
transducers are used to represent binary relations between pairs of
strings (specifically, rational transductions). The weights can be used
to represent the cost of taking a particular transition.
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