It's obvious

[Jim Parish]

Joel S. Berson wrote:
> I have now recalled another "it's obvious" tale, told to or read by me
> I cannot recall when:
>
> The professor of mathematics is at the lecture hall blackboard,
> writing out a proof.  As he writes one step, he remarks "this step is
> obvious".  He looks again, pauses, steps back, and pauses some more.
> Then he says "excuse me" and leaves the room.  About 40 minutes later
> he returns, says "yes it's obvious", and continues writing the proof.
>
> I don't think I'm confusing this with a cartoon; my visual memory is
> pretty strong.

That story was current among the grad students in math at the
University of Chicago around 1980. As I recall, one of them claimed to
have been present when it happened, but he made quite a number of,
um, interesting claims....

Speaking as a mathematician, I should point out that "trivial" and
"obvious" have special meanings in our argot; they pertain to how
closely an assertion follows from results, or by methods, that every
mathematician is expected to be familiar with. (Of course, that last is
still contextually variable; an acquaintance of mine once had a
conversation with Charles Fefferman - one of the top mathematicians in
his field - in which Fefferman made a certain claim. My friend asked, "Is
that true?" Fefferman replied, "Of course; everyone knows that!" Well,
everyone who talks advanced mathematics with Charles Fefferman,
maybe....)

Jim Parish

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