In Appendix B "Jensen's inequality" of "Information theory and coding" by McEliece, the abbreviation (NB) is repeatedly used in the statements of theorems B.1 and B.2. However I cannot locate where in the book the abbreviation is explained.
Theorem B.1 Let I be a discrete set of integers, and let $p_i,i\in I$, be a set of positive (NB) real numbers such that $\sum_{i\in I}p_i=1$. If $q_i$ is any other set of nonnegative (NB) real numbers....
Similarly for theorem B.2.
There is nothing in the index labelled "NB", and even downloading a scan and searching for NB got me nowhere. I also looked in Feller's book on probability which McEliece uses as a reference, but could not find it.
The only thing that NB usually stands for seems to be "Nota Bene" or "note well", so is this just an alert to the reader?