In an alphabetic writing system, a silent letter is a letter that, in a particular word, does not correspond to any sound in the word's pronunciation. Phonetic transcriptions that better depict pronunciation and which note changes due to grammar and proximity of other words require a symbol to show that the letter is mute. Handwritten notes use a circle with a line through it and the sound is called "zero"; It resembles the symbol for the "empty set", but must not be confused with the Danish and Norwegian letter Ø. In printed or computer's graphic presentation, using the IPA system, the symbol is used.