[Cryptography] paragraph with expected frequencies

[Sidney Markowitz]

It would be better to teach the how statistics provide usefully approximate
results rather than faking a perfect match to some commonly quoted frequency.

Here is one interesting contrast of letter frequencies from a few different
sources, quoted from the multi-language examples at
http://www.bckelk.ukfsn.org/words/etaoin.html

  David Copperfield          etaoinhsrdlmuwycfgpbvkxjqz
  Pride and Prejudice        etaoinhsrdlumcywfgbpvkzjxq
  Wuthering Heights          etaonihsrdlumcyfwgpbvkxjqz
  Vanity Fair                etaonhsirdlumcwfgypbvkjqxz
  Gulliver's Travels         etoainshrdlmucfwygpbvkxjqz
  Alice in Wonderland        etaoihnsrdluwgcymfpbkvqxjz

  Inaugural speeches:

  Reagan                     etonarishdlumwcfgpybvkjxzq
  Obama                      etoarnsihdlucwfmgpybvkjqzx

  British National Corpus    etaoinsrhldcumfpgwybvkxjqz
  (90 million words of UK English)

  Brown corpus               etaoinsrhldcumfpgwybvkxjqz
  (one million words of US English)

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