The nucleotides A,C,G,T were given indicator values as follows:
data(DNA)
-- G. G. Towell and J. W. Shavlik and M. W. Craven, 1991; "Constructive Induction in Knowledge-Based Neural Networks", In Proceedings of the Eighth International Machine Learning Workshop, Morgan Kaufmann.
-- G. G. Towell, 1991; "Symbolic Knowledge and Neural Networks: Insertion, Refinement, and Extraction", PhD Thesis, University of Wisconsin - Madison.
-- G. G. Towell and J. W. Shavlik, 1992; "Interpretation of Artificial Neural Networks: Mapping Knowledge-based Neural Networks into Rules", In Advances in Neural Information Processing Systems, volume 4, Morgan Kaufmann.