Tandem compliment repeats are an example of a (multiple) context-
sensitive language (much like rna pseudoknots in structure.) An
example is ATGC-TACG where A in the first set is bound to T in the
second set...
I've released a small app that explores the language of them in raw
dna data that can be found here: http://www.rnaparse.com/Downloads.html
