### Re: the blackboard vs. presentation debate

I came back from a couple of conferences not long ago. Here is something non-mathematical that I learned, which changed my opinion regarding the title. What I learned can be described by the following exact sequence:

$0 \rightarrow I \rightarrow T \rightarrow C \rightarrow 0$

Here, $I$ represents an Israeli speaker, $T$ represents the talk, into which the Israeli speaker injects all his knowledge into, and $C$ represents a mostly Chinese audience, onto which the talk is mapped surjectively. Unfortunately, the kernel of the map from $T$ to $C$ is precisely the image of the map from $I$ to $T$, so really all that the audience is left with at the end is everything in the talk modulo what the speaker was trying to say.

Paul Erdos is known for saying that the international language of Mathematics is broken English. It is true that the broken English spoken by a Hungarian, a Russian, or an Israeli are almost the same language. But there are other countries where a very different dialect of broken English is spoken. An Israeli breaks English in directions orthogonal to the way a Chinese would.

Corollary: The next time that I go to China (if they ever invite me again!!) I will prepare a presentation.

Besides the fact that I gave a talk that I thought was incomprehensible to many people, the conference was very interesting, and I met great people, and received the finest hospitality I ever did.