The Vault Breaker

hard · 4 inputs, 2 outputs · allowed gates: NAND · best known: 13 gates (not proved minimal)

To crack the SAFE, you must align the GEAR and the LOCK. The ALARM sounds if both GEAR and LOCK are active, or if the lever is set but NOT the sensor.

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The truth table

Inputs on the left, outputs on the right. A circuit solves the puzzle when it reproduces every row.

What the table tells you

• ALARM is 1 in 7 of the 16 rows. Every input matters: for each one there is a row where flipping it changes ALARM.
• SAFE is 1 in 1 of the 16 rows, so it is a single AND-shaped condition: one exact combination of the inputs. Every input matters: for each one there is a row where flipping it changes SAFE. The rows that turn it on: GEAR=0, LOCK=0, LEVER=0, SENSOR=0.

The smallest known circuit: 13 gates

As a formula, one line per output:

• ALARM = ((GEAR AND LOCK) OR (LEVER AND NOT SENSOR))
• SAFE = NOT (((GEAR OR LOCK) OR LEVER) OR SENSOR)

As a netlist, in the order you would wire it. Each g is one gate; the last lines say which signal drives each output.

1. g1 = GEAR NAND LOCK
2. g2 = SENSOR NAND SENSOR
3. g3 = GEAR NAND GEAR
4. g4 = LOCK NAND LOCK
5. g5 = LEVER NAND LEVER
6. g6 = LEVER NAND g2
7. g7 = g3 NAND g4
8. g8 = g1 NAND g6
9. g9 = g7 NAND g7
10. g10 = g5 NAND g9
11. g11 = g10 NAND g10
12. g12 = g2 NAND g11
13. g13 = g12 NAND g12
14. ALARM = g8
15. SAFE = g13

The search ran out of budget before it could rule out every smaller circuit, so 13 is the best anyone found, not a proof. If you build it in fewer, the leaderboard records it. Gates that do not feed an output are never counted.

Leaderboard for the day

Nobody posted a result on the day. The circuit above is the reference.

← #2 The Lighthouse Beacon · #4 The Bakery Oven Timer →

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