There is also the singular case of Yahya ould Hamidoune, the Mauritanian mathematician. In fact, ould is not a name: it just means 'the son of'. It is used in the same spirit of the Italian patronyms 'de' or 'de' ' (as in Bruno de Finetti or Lorenzo de' Medici), so it should be treated in the very same way. However, most of Hamidoune's papers are cited (or even signed by Hamidoune himself!) as if 'Yahya' and 'ould' were two first names, which is why you will typically read 'H. O. Hamidoune' or 'Hamidoune, H. O.' in bibliographies. (In still other cases, matters are just cut short by dropping the 'ould'.)
In an ideal world, I think the mistake (if you also take it as such) should be definitely fixed: Hamidoune's papers would be indexed as 'H. ould Hamidoune' or 'ould Hamidoune, H.' (depending on the journal style), and ordered by making reference only to 'Hamidoune' (if they have to be ordered alphabetically). But I'm urged to be realistic: this won't happen for many reasons.