Improved lower bound on the Shannon capacity of C7

An independent set with 108 vertices in the strong product of four 7-cycles (C-7 boxed times C-7 boxed times C-7 boxed times C-7) is given. This improves the best known lower bound for the Shannon capacity of the graph C-7 which is the zero-error capacity of the corresponding noisy channel. The search was done by a computer program using the "simulated annealing" algorithm with a constant time temperature schedule. (C) 2002 Elsevier Science B.V. All rights reserved.