Builds a compact subword vocabulary by starting with characters, counting adjacent token pairs, and repeatedly merging the most frequent pair. This reduces sequence length while retaining a small vocabulary. section 14.2.2
Merging a toy corpus
For “the quick brown fox”, “the slow brown fox”, and “the quick brown foxhound”, the pair “o w” occurs most often. Merging it creates “ow”; later merges can turn “ow” plus “l” into “low”. The process continues until the desired vocabulary size is reached. section 14.2.2










