unique / anonymous / nameless number.
Useful for xi subscripts to indicate the attached cmavo has a separate index from any other (e.g. «daxixo'e'o» to indicate a localized ‘there is / some’, without keeping track of an index pool; this can be repeated for multiple anonymous das), like anonymous, nameless lambda functions. Etymology: xo'e and po'o (or possibly xo'e and di'o). See also: da'au (proposed equivalence: «da'au» ＝＝ «daxixo'e'o»).