sentences:  While it is not generally used in formal writing, it is used in mathematics and shorthand.According to Cajori, "A History of Mathematical Notations," Johann Rahn used both the "therefore" and "because" signs to mean "therefore"; in the German edition of "Teutsche Algebra" (1659) the "therefore" sign was prevalent with the modern meaning, but in the 1668 English edition Rahn used the "because" sign more often to mean "therefore".Other authors in the 18th century also used three dots in a triangle shape to signify "therefore", but as with Rahn, there wasn't much in the way of consistency as to how the triangle was oriented; "because" with its current meaning appears to have originated in the 19th century.