# So what was Dr. Blind’s question, then?

I suspect I must have blogged this quote already, but since I can’t find such a post, I may as well repeat it.

Dr Blind (pronounced ‘Blend’) was about ninety years old and had taught, for the past fifty years, a course called ‘Invariant Subspaces’ which was noted for its monotony and virtually absolute unintelligibility, as well as for the fact that the final exam, as long as anyone could remember, had consisted of the same single yes-or-no question. The question was three pages long but the answer was always ‘Yes.’ That was all you needed to know to pass Invariant Subspaces.

He was, if possible, even a bigger windbag than Dr Roland. Together, they were like one of those superhero alliances in the comic books, invincible, an unconquerable confederation of boredom and confusion. I murmured an excuse and slipped away, leaving them to their own formidable devices.

(From Donna Tartt’s excellent novel The Secret History, which has nothing to do with mathematics.)

**Update 25th Jan 2013:** Professor Blind, meet Professors Cowen and Gallardo.

**further update 5th Feb 2013:** As you were; nothing to see here; move along.

The question was as follows: “Consider the following ‘proof’ of that every operator on a Hilbert space has an invariant subspace: ….”

then a three page argument, followed by the words “Is there a gap in the above proof?”

Excellent suggestion!

I think many might find the fable about a table given on

http://pages.bangor.ac.uk/~mas010/carpntry.htm

relevant. Or not?