n-Merge Conversion: placed immediately before a selbri, merges x4 and all xa places.
In "xa", "a" is not a variable; "xa" refers to any sumti slot(s) after the first n, where n is a function of the brivla (and is not defined for some brivla), such that it/they is/are part of an open-ended or arbitrarily large relation of mutually similar 'form' (possibly by analogy); for example, all sumti slots of "jutsi" except jutsi1 are xa-type slots. See also: "ze'e'i", "xe'e'o".