The Arabic letter "šīn" was an acronym for "something" ( "šayʾ(un)" ) meaning the unknown in algebraic equations. In the transcription into Spanish, the Greek letter "chi" (χ) was used which was later transcribed into Latin "x". According to some sources, this is the origin of "x" used for the unknown in the equations. However, according to other sources, there is no historical evidence for this. In Modern Arabic mathematical notation, "sīn", i.e. "šīn" without its dots, often corresponds to Latin "x".