constrained systems, deterministic encoders, finite-state encoders, input-constrained channels, nested encoders An input-constrained channel, or simply a constraint, is a set of S of words that is generated by a finite labeled directed graph. In the context of coding, the study of constraints mainly aims at designing encoders that map unconstrained input words into words of S in a lossless manner. In most applications, the encoders are finite-state machines that map in each time slot a fixed-length input block into a fixed-length channel block, and decoding is carried out by looking ahead at finitely-many upcoming channel blocks. The state diagram of a finite-state encoder provides a graph presentation of that encoder. In the special case where this graph is (output) deterministic, only the current channel block is needed for decoding the current input block.