In the local comparison, given some string …wxyz…, in order for a word boundary to be inserted between x and y, the predictability measure for xy must be lower than both that of wx and of yz. It follows that neither wx nor yz can have word boundaries between them, since they cannot simultaneously have a lower predictability measure than xy. This means that, within an utterance, word boundaries must have at least two segments between them, so this heuristic will not correctly segment utterance-internal one-phoneme words. 3 Granted, only a few one-phoneme word types exist in either English or Greek (or other languages). However, these words are often function words and so are less likely to appear at edges of utterances (e.g., ends of utterances for articles and prepositions; beginnings for postposed elements). Neither<cite> Brent's (1999a)</cite> implementation of Saffran's et al. (1996) heuristic nor utterance-boundary heuristic can explain how these might be learned.