kazmi experimental gismu

x1 (li) is the cardinality of set x2 (set)

Exactly equivalent to nilzilcmi except in morphology. But cardinality is a pretty fundamental thing in mathematics (in some sense, even more fundamental than natural numbers), so it arguably deserves a gismu; this will also shorten many lujvo which should use a word for cardinality. The second terbri should technically be filled by a set, but other structures could probably be acceptable; these might include groups and other algebraic structures, multisets, lists, classes, vel sim. ci'i alone (without being followed by another (integer-representing) digit) indicates an infinite cardinality but not which one; beware the assumption of the Axiom of Choice or Generalized Continuum Hypothesis.

In notes:

x1 is an object described as x2, x3, ... (termset representing serializable tree structure compatible with JSON format of attribute-value pairs).