ranking an album 0.5 requires at least 0 listenings
ranking an album 1.0 requires at least 1 listening
ranking an album 1.5 requires at least 1 listening
ranking an album 2.0 requires at least 2 listenings
ranking an album 2.5 requires at least 3 listenings
ranking an album 3.0 requires at least 5 listenings
ranking an album 3.5 requires at least 8 listenings
ranking an album 4.0 requires at least 13 listenings
ranking an album 4.5 requires at least 21 listenings
ranking an album 5.0 requires at least 34 listenings

ranking tracks of a 0.5 album requires at least 1 listening
ranking tracks of a 1.0 album requires at least 1 listening
ranking tracks of a 1.5 album requires at least 2 listenings
ranking tracks of a 2.0 album requires at least 3 listenings
ranking tracks of a 2.5 album requires at least 5 listenings
ranking tracks of a 3.0 album requires at least 8 listenings
ranking tracks of a 3.5 album requires at least 13 listenings
ranking tracks of a 4.0 album requires at least 21 listenings
ranking tracks of a 4.5 album requires at least 34 listenings
ranking tracks of a 5.0 album requires at least 55 listenings


album score is always between the 33% quantile and the maximal score among all track scores.


album comprehention stages:
1) plan to listen
2) trying to comprehend
3) familiar
4) taking a closer look
5) well familiar
6) preparing to rate tracks
7) completed

3-rd, 5-th and 7-th stages are terminal.

album has rating iff its stage >= 3
album has track ratings iff its stage >= 7