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An upper bound on the feedback capacity of unifilar finite-state channels (FSCs) is derived. A new technique, called the Q-contexts, is based on a construction of a directed graph that is used to quantize recursively the receiver's output sequences to a finite set of contexts. For any choice of Q-graph, the feedback capacity is bounded by a single-letter expression, C_fb≤ I(X,S;Y|Q), where the supremum is over P_X|S,Q and the distribution of (S,Q) is their stationary distribution. It is shownarXiv:1604.01878v1 fatcat:gj6cau7vlzd5zedamgcthxs6aa