  The Burrows-Wheeler-Transform (BWT) is an invertible permutation of a text
known to be highly compressible but also useful for sequence analysis, what
makes the BWT highly attractive for lossless data compression. In this paper,
we present a new technique to reduce the size of a BWT using its combinatorial
properties, while keeping it invertible. The technique can be applied to any
BWT-based compressor, and, as experiments show, is able to reduce the encoding
size by 8-16 % on average and up to 33-57 % in the best cases (depending on the
BWT-compressor used), making BWT-based compressors competitive or even superior
to today's best lossless compressors.
