Bibliography section, some references cannot be found

hi.

while reading this[1],
<< More information about partial indexes can be found in [ston89b],
[olson93], and [seshadri95].
I googled around, still cannot find [olson93] related pdf or html link.

in [2],
I found out
[ong90] “A Unified Framework for Version Modeling Using Production
Rules in a Database System”. L. Ong and J. Goh. ERL Technical
Memorandum M90/33. University of California. Berkeley, California.
April, 1990.
related link is
https://www2.eecs.berkeley.edu/Pubs/TechRpts/1990/1466.html

an idea:
In case these external links in
(https://www.postgresql.org/docs/current/biblio.html) become dead
links,
we can send these external pdf or html files in the mailing list for
archive purposes.

[1] https://www.postgresql.org/docs/current/indexes-partial.html
[2] https://www.postgresql.org/docs/current/biblio.html