NOT.4:5.2 - Compress a sequence while preserving its order

A notation describes ordered cues A and B. The sequence A; B; A; B is to be shortened without changing the order of cues. Define repeat 2 { E } to expand into two copies of the entire finite sequence E, preserving its order. Then:

A; B; A; B  ->  repeat 2 { A; B }

Expansion returns A, B, A, B. The third cue remains A. A reader changing B in every repeated unit can now change it once in the repeated body. If only the final B must change to C, expand or separate that occurrence: A; B; A; C. The earlier abbreviation no longer expresses the intended two identical units.

The tempting form repeat 2 { A }; repeat 2 { B } expands to A, A, B, B. It preserves counts but changes the third cue to B. Counts are insufficient for the selected ordered reading. No rule for exchanging cues was supplied.

This notation states cue order. If intervals, accents or bodily actions distinguish the repetitions, retain those distinctions in E or choose a different abbreviation. The order-preservation result alone supplies no claim about those further observations.