21
$\begingroup$

Some people in the American Senate are working for secret organizations. Some work for the Illuminati, some work for the Knights Templar, and some work for both. The are also innocent citizens who are unaware of these organizations. Both organizations meet in secret with masks and hoods respectively, so that the members cannot identify one another outside the headquarters.

One senator, Reginald, works for the Illuminati, and likes his colleagues, but prefers the Knights Templar headquarters. He finds an arcane rule in the ancient texts, that gives him a brilliant idea. He will turn each Templar into an Illuminati and each Illuminati into a Templar. That way, he becomes a Templar and gets to hang out in their headquarters, but with his old friends.

The rule goes as follows: If Reginald speaks the name of a senator in the senate and touches his left shoulder, that senator becomes a member of the Illuminati, if he touches his right shoulder, the senator becomes a member of the Knights Templar.

This mechanism is meant to be used by people who know to which group the senator in question belongs. To avoid abuse by people using it blindly, the following rules are added:

  • If a citizen is named, he remains a citizen.
  • If the senator was already in the group he is assigned to but not in the other, things stay as they are
  • If the senator was not in the group he is assigned to, but he is in the other, he becomes a member of both groups.
  • If the senator was already a member of both groups, he is removed from the group he was supposed to be assigned to.

Can Reginald, who does not know to which group any Senator belongs, implement his plan, and turn every Illuminati into a Templar Knight and vice versa? The shared members should end up shared, and the citizens must never, even temporarily, become part of either group.

Improve this question
$\endgroup$
5
  • $\begingroup$ And then he is immediately kicked out because everyone in either group knows he is Illuminati and wants the nicer office. No one knows that he keeps coming to the meetings though. $\endgroup$
    – kaine
    Commented Oct 24, 2014 at 18:12
  • 1
    $\begingroup$ The two points "Citizens cannot be added to either group by this procedure" and "the citizens must never, even temporarily, become a part of either group" are slightly problematic. It's not clear whether the "cannot" is a matter of effectiveness -- the tap does nothing -- or of permissibility -- if you try, Yog Sothoth eats your brain/Baphomet owns your soul. If the latter, then the puzzle seems insoluble. If the former, the warning about citizens never joining a group is superfluous. (Perhaps it's intended to be obfuscatory?) $\endgroup$
    – jscs
    Commented Oct 24, 2014 at 19:30
  • 1
    $\begingroup$ Is Reginald required to touch his own shoulders? $\endgroup$
    – tobyink
    Commented Oct 24, 2014 at 20:26
  • $\begingroup$ @tobyink It's a free country, but he only invokes the rule when he touches his own shoulder (and speaks the name). $\endgroup$
    – Peter
    Commented Oct 24, 2014 at 21:56
  • $\begingroup$ @JoshCaswell Yeah, it was meant to be a little obfuscation. I've edited the first rule a little. $\endgroup$
    – Peter
    Commented Oct 24, 2014 at 21:58

1 Answer 1

Reset to default
22
$\begingroup$

For each member of the senate, say the name and touch the shoulders in LRL order (or RLR)

For Illuminati (L), first touch (L > L) will do nothing, second one (R > LR) will make senator both, then third (L > R) will remove it, turning an Illuminati (L) to Templar (R).

For Templars (R), (L > LR), (R > L), (L > L), turning a Templar (R) to Illuminati (L).

For both (LR), (L > R), (R > R), (L > LR), keeping as both.

Normal people will just wonder why all the shoulder tapping.

Improve this answer
$\endgroup$
1
  • 1
    $\begingroup$ I was able to come up with the same answer using brute force. I am wondering though if there exists some intuition to this answer. Like looking at the solution from AND OR gates' perspective, truth table perspective, finite state machine perspective or from the perspective of some other intuitive method. $\endgroup$
    – Hemant Agarwal
    Commented Jun 12, 2023 at 23:42

Not the answer you're looking for? Browse other questions tagged or ask your own question.