Radio rotation audit

Audit a radio station's playlist log and report every song that breaks the artist-separation rule.

log lists what went out on air, in order. Each entry is either the text "[ad]" (an ad break) or the artist credit of one song. A credit holds one or more artist names joined by " & ", for example "Nova Reyes & Kite" credits two artists. Names are compared ignoring letter case, so "KITE" and "Kite" are the same artist.

The station's rule: an artist must not be heard again until at least gap other songs have been played since their last appearance. In other words, a song is a violation if any artist credited on it was credited on any of the previous gap songs. Ad breaks are not songs: they do not count toward the gap and they do not reset anything. A song that is a violation still counts as having been played, so it also blocks the artists credited on it for the songs that follow.

Input: log, the on-air entries in order, and the separation gap.

Output: a list of the 1-based positions in log (ads occupy positions too) of every violating song, in increasing order. Return an empty list if there are none, including when gap is 0 or the log is empty.