In German orthography, the umlauted vowels ä, ö, and ü historically arose from "ae", "oe", "ue" ligatures (strictly, from superscript "e", viz. "aͤ", "oͤ", "uͤ"). It is common practice to replace them with "ae, oe, ue" digraphs when the diacritics are unavailable, for example in electronic conversation. Phone books treat umlauted vowels as equivalent to the relevant digraph (so that a name Müller will appear at the same place as if it were spelled Mueller; German surnames have a strongly fixed orthography, either a name is spelled with "ü" or with "ue"); however, the alphabetic order used in other books treats them as equivalent to the simple letters "a", "o" and "u". The convention in Scandinavian languages and Finnish is different: there the umlaut vowels are treated as independent letters with positions at the end of the alphabet.