Type math? In 1955? That would have required specialized equipment, possibly a secretary. Nash clearly believed that the contents were of national security interest.
Maybe the fact that it is not typed is a key to it's hidden meaning. Maybe there are reasons that only parts of this letter are clarified...
In all seriousness, this pdf basically unreadable. It would be nice if there was a readable version available to the general public. If there is one, please let me know because this is very interesting.
The first time I looked at this pdf there were blocks of printed text all over the place that floated over the handwritten text. By floating over I mean literally covering the written text. After I read your comment I looked at it again and it was simply the handwritten text.
I'm not sure if my pdf reader confused things or the nsa has a special redirect for me. But the complete handwritten text is perfectly readable to me now. I'm not sure what I saw before, but it was odd...
http://www.nsa.gov/public_info/_files/nash_letters/nash_lett...