December 10, 1958
Dear Francis:
I met Igor Tamm at a reception last night and he proved a remarkably lively and linguistically accomplished fellow, quite extraordinary among the Russians I've ever met.  He is also remarkably interested and well informed about genetics, far more than any Russian biologist I've encountered.
He was quizzing me on triplet codes and raised the question of redundancy in the complement, which I thought I had long since raised with and had quieted by you, but I couldn't reproduce the agreement.
Briefly, in a complementary double helix, does a triplet carry 5 bits or 6?  His argument was that the sets:
[figure]
i.e., ABC = C'B'A' and insisted there was no exception on the grounds of steric asymmetry--i.e., the double helix has the same sense when inverted.
I could hardly think you had overlooked this point; Tamm brought it up in connection with the utility of the 20 meaningful triplets in a comma-less code.  The steric argument is the one I can't intuitively be quite sure of without the models so the quickest answer seemed to be to ask you directly.
Fred Sanger will give you all the intimate and gruesome details of the week here.  One minor calamity averted when Ed Tatum finally showed late last evening having been fogbound in Paris.
All best wishes
Joshua
Have a fine time at Cambridge and we look forward to seeing you in July.