[Text available only in English] In mathematics, x is commonly used as the name for an independent variable or unknown value. The usage of x to represent an independent or unknown variable can be traced back to the Arabic word šay' شيء = “thing,” used in Arabic algebra texts such as the Al-Jabr. It was subsequently taken into Old Spanish with the pronunciation /ʃei/, which was written xei and soon habitually abbreviated to ‪x‬. (The Spanish pronunciation of ⟨x⟩ has...