are 19th-century books in which the writer uses neither "¡" nor "¿". Adoption Some writers omit the inverted question mark in the case of a short unambiguous question such as: ("Who comes?"). This is the criterion in Galician and formerly in Catalan. Certain Catalan-language authorities, such as Joan Solà i Cortassa, insist that both the opening and closing question marks be used for clarity. The current IEC prescription for Catalan is not to use the inverted marks. Some Spanish-language writers, among them Nobel laureate Pablo Neruda (1904–1973), refuse to use the inverted question mark. It is common on social media to omit the inverted question mark since it saves typing time. Some also use the ending symbol for both beginning and ending, like this: . Others may even use both the opening and closing question marks, but at the end of the sentence, giving or . Given the informal setting, this might be unimportant; however, teachers see this as a problem, fearing and claiming that contemporary young students are inappropriately and incorrectly extending the practice to academic homework and essays. (See .) Mixtures It is acceptable in Spanish to begin a sentence with an opening inverted exclamation mark ("¡") and end it with a question mark ("?"), or vice versa, for statements that are questions but also have a clear sense of exclamation or surprise such as: ("And who do you think you are?!"). Normally, four signs are used, always with one type in the outer side and the other in the inner side (nested) (, ) Unicode 5.1 also includes , which is an inverted version of the interrobang, a nonstandard punctuation mark used to denote both excitement and a question in one glyph. It is also known as a "gnaborretni" () (interrobang spelled backwards). Computer usage Encodings and are both located within the Unicode Common block, and are both inherited from ISO-8859-1: The characters also appear in most extended ASCII encodings. In Windows, an inverted question mark is valid in a file or directory name, whereas the normal question mark is a reserved character which cannot be used. Typing the character and are available in all keyboard layouts for Spanish-speaking countries. Smart phones typically offer these if you hold down or in the on-screen keyboard. Auto-correct will often turn a normal mark typed at the start of a sentence to the inverted one. On systems with an AltGr