 Similarly, difficult-to-read kanji such as "gan" ("cancer") are often written in katakana or hiragana.Katakana is also used for traditional musical notations, as in the "Tozan-ryū" of "shakuhachi", and in "sankyoku" ensembles with "koto", "shamisen" and "shakuhachi".Some instructors teaching Japanese as a foreign language "introduce "katakana" after the students have learned to read and write sentences in "hiragana" without difficulty and know the rules."