This post made me wonder. Is seen س the standard way to represent an unknown variable in Arabic? And in mathematics? It's funny because I know the X that is used in Western languages to represent an unknown variable -- first in mathematics and later elsewhere -- has its origins in Arabic! I was told that the Arabic mathematicians used to put شيء 'something' as a variable. When the Arabic knowledge was exported to Iberia, the sheen ش was replaced by <X> which was the grapheme for /š/ in the area in those days (still to be found sometimes in Portuguese and Catalan if I'm not mistaken). Should someone have made me guess how a variable would be represented in Arabic, I would've guessed with a sheen. But now I see elroy use a seen for it, and I wonder if that is a more common way maybe? Or maybe there is simply no common way? Thank you in advance!