Magic & Math with Cards

Lecture 30 · Performance

The deck becomes a lie detector

Video in production

This lecture is still face down. Its script is written; filming and animation are under way.

Meanwhile, play the trick

What you will learn

Perform and decode a Curry/Gilbreath colour-claim routine with explicit observed-data and claim channels.

The trick in this lecture The Lie Detector Call out the colour of each card you look at, truthfully or not. The verdict is right every time. Play the trick

Before this lecture

In this lecture

An outline of the lecture, scene by scene, with the statements that appear on screen. It follows the draft script, so details may change in production.

  1. Prepare and divide complementary packets

    At the table
    • One legal shuffle
    • Alternate left / right

  2. Record actual observations

    At the table
    • Observation ≠ claim
    • Record actual colour after reveal

  3. Test arbitrary claims

    At the table
    • Claim → verdict → reveal

  4. Prove partner alignment

    • Aligned pairs are opposite
    • Both receiving piles reverse

  5. Separate observations from claims

    • Observed actual → opposite expected
    • Claim compared separately

  6. Write the decoder

    • BLACK = 0; RED = 1
    • Expected = 1 − a
    • TRUE iff q = 1 − a

  7. Diagnose invalid correspondence

    • Same positions, same reading direction
    • Used cards leave the packet

  8. Play and retrieve

    • Record → Test → Audit
    • Explain the correspondence

Companion interactive

Make arbitrary claims and explain the decoder's verdicts.

The trick page is this lecture’s companion: be the spectator, lift the curtain to step through why it works, try the challenge, then learn the handling.

Open The Lie Detector

Sources

How these sources were used
  • Persi Diaconis and Ron Graham, Magical Mathematics: Curry presentation adapted to sixteen cards and an explicit audited scorekeeper. Separate observed colours from arbitrary spoken claims.