  This survey stems from Amnon Neeman's lecture series at Ohakawa's memorial
workshop. Starting with Ohakawa's theorem, this survey intends to supply enough
motivation, background and technical details to read Neeman's recent papers on
his "approximable triangulated categories" and his $D_{coh}^b(X)$ strong
generation sufficient criterion via de Jong's regular alteration, even for
non-experts.
  At the same time, the author, who happens to be a coorganizer of this
workshop and an editor of the follow-up proceedings to be published as a series
in Springer Proceedings in Mathematics and Statistics, repeatedly mentioned
rich mathematical interaction with other papers in the proceedings, whenever
appropriate.
