The observation by Heinz (2009), which we may repeat from the pattern formula in Example (15), is that each and every component of a regular expression describing a stress grammar should be unique.
if the neighborhood were defined as a single syllable, we would not predict to find a language that uses the same building blocks {(σσ), [(σσ)] 0 , [σ]}, but in a pattern like Example (16), where the same block is used at multiple positions in the formula: It is entirely possible for such a language to exist and be learned, but this must mean that such a learner is using a different (i.e., wider) syllable span for its definition of phonological neighborhood.