proper: On the other hand, the following phonetic letters have Unicode representations separate from their Greek alphabetic use, either because their conventional typographic shape is too different from the original, or because they also have secondary uses as regular alphabetic characters in some Latin-based alphabets, including separate Latin uppercase letters distinct from the Greek ones. The symbol in Americanist phonetic notation for the voiceless alveolar lateral fricative is the Greek letter lambda , but in the IPA. The IPA symbol for the palatal lateral approximant is , which looks similar to lambda, but is actually an inverted lowercase y. Use as numerals Greek letters were also used to write numbers. In the classical Ionian system, the first nine letters of the alphabet stood for the numbers from 1 to 9, the next nine letters stood for the multiples of 10, from 10 to 90, and the next nine letters stood for the multiples of 100, from 100 to 900. For this purpose, in addition to the 24 letters which by that time made up the standard alphabet, three otherwise obsolete letters were retained or revived: digamma for 6, koppa for 90, and a rare Ionian letter for [ss], today called sampi , for 900. This system has remained in use in Greek up to the present day, although today it is only employed for limited purposes such as enumerating chapters in a book, similar to the way Roman numerals are used in English. The three extra symbols are today written as , and respectively. To mark a letter as a numeral sign, a small stroke called keraia is added to the right of it. Use by student fraternities and sororities In North America, many college fraternities and sororities are named with combinations of Greek letters, and are hence also known as "Greek letter organizations". This naming tradition was initiated by the foundation of the Phi Beta Kappa Society at the College of William and Mary in 1776. The name of this fraternal organization is an acronym for the ancient Greek phrase Φιλοσοφία Βίου Κυβερνήτης (Philosophia Biou Kybernētēs), which means "Love of wisdom, the guide of life" and serves as the organization's motto. Sometimes early fraternal organizations were known by their Greek letter names because the mottos that these names stood for were secret and revealed only to members of the fraternity. Different chapters within the same fraternity are almost always