x1 is the learning process / overall learning event of [learner] x2 on topic x3, including facts / subtopics x4.
Also: x2 is a x3-learner; x3 covers topics x4. Describes the whole learning process, as opposed to 'atomic' knowledge acquisition, as implied by cilre; that process can even span years (if not x2's life). The 'atoms' can be drawn out of this word with x4, which can be a du'u abstraction (which really is cilre2), but also a smaller 'molecule' described with si'o (or not). Borrowing from Japanese (勉強).