Re earlier discussion, while looking up the zener, I passed across Motorola's
section on thyristors:
For Motorola at least, they treat thyristors as a class of devices ("triggerred
switches"), including both SCRs and TRIACs. It is somewhat ambiguous in the
writing as to whether they consider DIACS, UJTs, PUTs, etc. to be thyristors,
but they are all listed and described in the thyristors section.