Exercise 1: Tracing a Single Keypress Through Enigma — Possible Solution
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The full path, in order:

1. A key is pressed, starting an electrical signal.
2. The signal enters the PLUGBOARD. If that letter is one of the
   ~10 cabled pairs, it is swapped for its partner letter; otherwise
   it passes through unchanged.
3. The signal enters the RIGHTMOST rotor and is substituted according
   to that rotor's internal wiring.
4. The signal enters the MIDDLE rotor and is substituted again.
5. The signal enters the LEFTMOST rotor and is substituted a third
   time.
6. The signal reaches the REFLECTOR, which sends it back the OTHER
   way through a fixed set of 13 letter pairs (never back to the same
   letter it entered on).
7. The signal re-enters the LEFTMOST rotor, this time travelling in
   reverse, and is substituted again (using the same wiring, but in
   the opposite direction).
8. The signal passes back through the MIDDLE rotor, again in reverse.
9. The signal passes back through the RIGHTMOST rotor, again in
   reverse.
10. The signal re-enters the PLUGBOARD, swapped again if applicable.
11. The signal reaches the LAMPBOARD and lights exactly one lamp —
    the ciphertext letter.

The signal passes through the rotor stack TWICE total: once travelling
outward (rightmost -> middle -> leftmost) on its way to the reflector,
and once travelling in the opposite direction (leftmost -> middle ->
rightmost) on its way back from the reflector.

WHY THIS WORKS AS AN ANSWER
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This reuses the chapter's own 11-step pathway diagram directly. The
"passes through the rotors twice, in opposite directions" detail is
the specific point the chapter calls out as making Enigma reciprocal
(the same settings both encrypt and decrypt) — and it's also exactly
the structural detail Exercise 2 and Chapter 4 build on to explain the
reflector's exploitable weakness.