crosses, the ten letters currently under examination.
(f) Miscellaneous facilities.
(i) A cut-out switch for each of the five impulses.
(ii) Set total for extensions such that Dragon does not stop unless there is
a minimum number of extensions. Switch 5 means 5, switches 5 and i means i .
(iii) Switch for use when setting tapes back, such that the recorded setting
of D remains stationary.
(g) Miscellaneous switches
Reset tape, Reset tape and wheels, reset X2, Mu, limitation, single step,
de-chi display cut-out, test, start-stop.
(h) Dragon 1
Always contracts a repeated letter.
(i) Dragon 3
A much larger machine; can deal with a 16 letter crib, or with two or three
shorter ones simultaneously. It can cope with a gap of up to 5 letters in the
crib, trying every possible number of extensions in the gap.
This is a "compatibility" gadget for attachment to Dragon [see 28B (d) ).
55B PR0TEUS (Fig 58(xxxi))
(a) Purpose and method
Proteus anagrams depths [ 28A(d)(ii)]
The given depth V is known to be the sum of two plain texts P(a) + P(b) .
It is expected that at some position one of these will be a very common group of
plain text letters, say one of the six commonest: this is called the crib, P(1);
and that at the same position the other is a fairly common group, one of several
hundred , called the dictionary P(2).
Then of course P(1) + P(2) + v = /.
What Proteus does is to add P(1), P(2), V in all positions looking for a
position where the sum is all /'s.
(b) Setting up, P(1), P(2), V .
(i) P(1) The crib has a length of seven or fewer letters and is set up by
plugging. Each letter has 6 jacks: a cross in the 6th means "ignore this letter".
Actually six cribs are set up and examined simultaneously but independently.
(ii) P(2) The dictionary is on a tape running on a Colossus bedstead, with