From
宋 计有功 《
唐诗纪事》: the Tang monk-poet
齐己 wrote a poem 《
早梅》 with the line '
前村深雪里,
数枝开' ('several branches in bloom').
郑谷 suggested changing
数枝 ('several branches') to
一枝 ('a single branch') to fit 'early plum.'
齐己 bowed in thanks, and
郑 was honored as his
一字师 - one-character master.