Artifact 4de2807375002a0483a23064a85fd2556fd312f7:
File
www/selfcheck.html
part of check-in
[6458f020fc]
- Change the spelling of "descendant" to use the -ant suffix everywhere,
including in the filename "descendant.c". The adjective form can be
spelled either -ant or -ent, but the noun form requires -ant, or so
says American Heritage.
by
drh on
2008-05-14 02:03:45.
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