An encoder for encoding input data to generate corresponding encoded data is provided. The encoder (10) is operable to process a sequence of elements in the input data from a first element thereof to a last element thereof. The elements have corresponding symbols. The encoder is operable to compute probabilities of symbols present in the sequence, wherein the probabilities of the symbols are computed while disregarding those elements of the sequence that have already been encoded into the encoded data. Moreover, the probabilities of the symbols are adaptively changed as the sequence of elements is progressively encoded into the encoded data. Furthermore, information describing the probabilities is delivered; optionally, the probabilities of the symbols are accompanied with additional information indicating how the probabilities are adaptively changing. There is also provided a decoder for performing an inverse of encoding performed by the encoder.