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Definition of a competing, alternative helix. Pictorial definition of a competing, alternative helix. The known base-pair between sequence positions i and 
has to have at least two other directly adjacent base-pairs within the known secondary structure (right) and the competing, alternative helix has to contain an alternative base-pair between sequence positions i and c (c is the competitor of ) which has to be contained within a helix of minimum stem length (left).
