Dumb question: What IS a trigraph?

[Walter Murray]

Doug Gwyn writes:

>In article <3566 at uwovax.uwo.ca> 2014_5001 at uwovax.uwo.ca writes:
>>Every so often someone mentions a trigraph.  What is a trigraph???

>There's one (the "???").  

Nope.  Doug must not have had his dpANS handy.  The "???" smells a
little like a trigraph, but it isn't one.  Of all three-character
sequences beginning with "??", only nine are trigraphs, and "???"
isn't one of them!

Walter Murray
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