Add more notes on what's notable about mnemonicode

README

@@ -7,6 +7,94 @@ back to data on the other side.
 
 For more information see <http://web.archive.org/web/20101031205747/http://www.tothink.com/mnemonic/>
 
+There are some other somewhat similar systems that seem less satisfactory:
+
+- OTP was designed for easy typing, and for minimizing length, but as
+  a consequence the word list contains words that are similar ("AD"
+  and "ADD") that are poor for dictating over the phone
+
+- PGPfone has optimized "maximum phonetic distance" between words,
+  which resolves the above problem but has some other drawbacks:
+
+  - Low efficiency, as it encodes a little less than 1 bit per
+    character;
+
+  - Word quality issues, as some words are somewhat obscure to
+    non-native speakers of English, or are awkward to use or type.
+
+Mnemonic tries to do better by being more selective about its word
+list.  Its criteria are thus:
+
+Mandatory Criteria:
+
+ - The wordlist contains 1626 words.
+
+ - All words are between 4 and 7 letters long.
+
+ - No word in the list is a prefix of another word (e.g. visit,
+   visitor).
+
+ - Five letter prefixes of words are sufficient to be unique. 
+
+Less Strict Criteria:
+
+  - The words should be usable by people all over the world. The list
+    is far from perfect in that respect. It is heavily biased towards
+    western culture and English in particular. The international
+    vocabulary is simply not big enough. One can argue that even words
+    like "hotel" or "radio" are not truly international. You will find
+    many English words in the list but I have tried to limit them to
+    words that are part of a beginner's vocabulary or words that have
+    close relatives in other european languages. In some cases a word
+    has a different meaning in another language or is pronounced very
+    differently but for the purpose of the encoding it is still ok - I
+    assume that when the encoding is used for spoken communication
+    both sides speak the same language.
+
+  - The words should have more than one syllable. This makes them
+    easier to recognize when spoken, especially over a phone
+    line. Again, you will find many exceptions. For one syllable words
+    I have tried to use words with 3 or more consonants or words with
+    diphthongs, making for a longer and more distinct
+    pronounciation. As a result of this requirement the average word
+    length has increased. I do not consider this to be a problem since
+    my goal in limiting the word length was not to reduce the average
+    length of encoded data but to limit the maximum length to fit in
+    fixed-size fields or a terminal line width.
+
+  - No two words on the list should sound too much alike. Soundalikes
+    such as "sweet" and "suite" are ruled out. One of the two is
+    chosen and the other should be accepted by the decoder's
+    soundalike matching code or using explicit aliases for some words.
+
+  - No offensive words. The rule was to avoid words that I would not
+    like to be printed on my business card. I have extended this to
+    words that by themselves are not offensive but are too likely to
+    create combinations that someone may find embarrassing or
+    offensive. This includes words dealing with religion such as
+    "church" or "jewish" and some words with negative meanings like
+    "problem" or "fiasco". I am sure that a creative mind (or a random
+    number generator) can find plenty of embarrasing or offensive word
+    combinations using only words in the list but I have tried to
+    avoid the more obvious ones. One of my tools for this was simply a
+    generator of random word combinations - the problematic ones stick
+    out like a sore thumb.
+
+  - Avoid words with tricky spelling or pronounciation. Even if the
+    receiver of the message can probably spell the word close enough
+    for the soundalike matcher to recognize it correctly I prefer
+    avoiding such words. I believe this will help users feel more
+    comfortable using the system, increase the level of confidence and
+    decrease the overall error rate. Most words in the list can be
+    spelled more or less correctly from hearing, even without knowing
+    the word.
+
+  - The word should feel right for the job. I know, this one is very
+    subjective but some words would meet all the criteria and still
+    not feel right for the purpose of mnemonic encoding. The word
+    should feel like one of the words in the radio phonetic alphabets
+    (alpha, bravo, charlie, delta etc).
+
 mnemonic.h	Header file
 mnemonic.c	Encoding/decoding and associated routines
 mn_wordlist.c	The word list itself