We present an efficient algorithm for determining whether all molecules in a combinatorial set of DNA or RNA strands are structure free, and thus available for bonding to their Watson-Crick
complements. This work is motivated by the goal of testing whether strands used in DNA computations or as molecular bar-codes
are structure free, where the strands are concatenations of short words. We also present an algorithm for determining whether
all words in S, for some finite set S of equi-length words, are structure-free.
This material is based upon work supported by the U.S. National Science Foundation under Grant No. 0130108, by the National
Sciences and the Engineering Research Council of Canada, and by the by the Defense Advanced Research Projects Agency (DARPA)
and Air Force Research Laboratory, Air Force Materiel Command, USAF, under agreement number F30602-01-2-0555.