x1 is a source language for Lojbanic gismu x2, contributing word x3 (zoi) to make it, which were adapted into the Lojban alphabet as x4 (lo'u or zoi), the language having weight in the algorithm x5 (li)
Named reference. It converts a sumti into another sumti. The converted sumti points to the referent the name of which is the referent of the unconverted sumti.