8. A system for improving the coding performance of adaptive data compression systems having unstable statistical properties in their probability estimation model contexts, comprising: means for expanding each probability estimation model context of M binary bits into a larger coding context with at least one additional bit concatenated onto the original M bits of the particular probability estimation model context where the concatenated bit is the one of two possible binary bits (1 and 0) resulting from the decision D(A) associated with a previous probability estimation model context made up of the identical M bits; and means for applying the selected coding context in compressing data.
15. A system as in claim 8 further comprising means for actuating said model context expanding means whenever unstable probability estimates are encountered during coding.