2022
MIPT - Kulapin - AISD 1st course ru of 14 parts
    https://www.youtube.com/playlist?list=PL4_hYwCyhAvZtI5h-e2FBGLiygrGDWji0
    ! 7... deleting from b-tree ...
2021
MIPT - Kulapin - AISD ru of 7 parts
    https://www.youtube.com/playlist?list=PLthfp5exSWEpsWdzRVWheiM6fiHVewnGF
    !!! need to look, Fenvick tree at the end