However, the ü is not used in other contexts where it represents a front high rounded vowel, namely after the letters j, q, x and y. For example, the sound of the word 鱼/魚 (fish) is transcribed in pinyin simply as yú, not as yǘ. This practice is opposed to Wade-Giles, which always uses ü, and Tongyong Pinyin, which always uses yu. Whereas Wade-Giles needs to use the umlaut to distinguish between chü (pinyin ju) and chu (pinyin zhu), this ambiguity cannot arise with pinyin, so the more convenient form ju is used instead of jü. Genuine ambiguities only happen with nu/nü and lu/lü, which are then distinguished by an umlaut diacritic.
Many fonts or output methods do not support an umlaut for ü or cannot place tone marks on top of ü. Likewise, using ü in input methods is difficult because it is not present as a simple key on many keyboard layouts. For these reasons v is sometimes used instead by convention. Occasionally, uu (double u), u: (u followed by a colon) or U (capital u) is used in its place.
