Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In a mathematical proof, the therefore sign (∴) is a symbol that is sometimes placed before a logical consequence, such as the conclusion of a syllogism.[citation needed] The symbol consists of three dots placed in an upright triangle and is read therefore. It is Unicode character U+2234 and on some systems may be entered using ALT-8756 (the decimal version of 2234). While it is not generally used in formal writing, it is often used in mathematics and shorthand. According to Cajori, A History of Mathematical Notations, the therefore sign was first used by Johann Rahn in 1659, in the original German edition of his book Teutsche Algebra.