The Puzzle of the Prankster Twins

logical riddles with no hockey knowledge required

I hesitate to use phrases like “greatest duo in history,” but have you heard of the Sedin Twins? They were:

  1. identical twin boys, Daniel and Henrik,
  2. who are now in the Hockey Hall of Fame,
  3. having played on the same NHL team for 17 years,
  4. and messed with people every chance they got — making them, by any objective standard,
  5. the greatest duo in history.
The Puzzle of the Prankster Twins

It’s like if two elite athletes happened to be Fred and George Weasley. Some fans insist they played at least one game with swapped jerseys. My favorite is this tale from Reddit, of a fan getting signatures on trading cards:

when I was a kid… my dad took me to the hotel they were staying at to get autographs….

A Sedin came out, and I held out both of their cards and asked which one he should sign. He signed Daniel….

Then 15 minutes later the other Sedin appeared, and I handed him Henrik’s card. “No, I’m Daniel” he said, but then I revealed that Daniel had already signed my card….

To this day I don’t know if the second Sedin was messing with me or if the first one had successfully trolled me and the second one just rolled with it.

In the replies, someone points out:

Either way, we can logically deduce that Henrik was the one doing the trolling. He’s either the one who came out first and signed Daniel’s card, or he’s the one who came out second and told you he’s Daniel.

Once I saw that comment, I couldn’t help myself. I may be a hockey fan, but I’m a math teacher first. (Or, rather: I may be a math fan, but I’m a hockey teacher first.) With apologies to Raymond Smullyan — and extra apologies to Henrik and Daniel — I present you these riddles…

Henrik and Daniel are identical twins. One always lies, and one always tells the truth, but you don’t know which is which. For each question: (a) can you tell which brother is speaking? (b) can you tell which brother is the liar?

1. “I am Daniel.”

2. “My brother is Daniel.”

3. “Henrik tells the truth.”

4. “Henrik lies.”

5. “Henrik would never say these words.”

6. “Only Henrik can say these words.”

7. “Daniel would call me honest.”

8. “Daniel would call me a liar.”

9. “My brother would say I’m Daniel.”

10. “My brother would say Daniel lies.”

11. “Both of us claim to be Henrik.”

12. Let’s say that Daniel is the truthteller. Can you think of something he might say that would reveal *both* that he is Daniel, *and* that he is telling the truth?

Solutions here. Spoiler-free discussion below; spoiler-filled discussion at the solutions page!