Please improve these comprehensions (was meaning of [ ])
Chris Angelico <rosuav at gmail.com> writes:
> On Thu, Sep 7, 2017 at 5:59 PM, Marko Rauhamaa <marko at pacujo.net> wrote:
>> Dennis Lee Bieber <wlfraed at ix.netcom.com>:
>>> On Wed, 06 Sep 2017 10:37:42 +0300, Marko Rauhamaa <marko at pacujo.net>
>>> declaimed the following:
>>>>Which reminds me of this puzzle I saw a couple of days ago:
>>>> 1 + 4 = 5
>>>> 2 + 5 = 12
>>>> 3 + 6 = 21
>>>> 8 + 11 = ?
>>>>A mathematician immediately comes up with a "wrong" answer.
>>> I'm coming up with "96", on the basis that the "+" is a
>>> placeholder for a non-standard operation
>> That's a mathematician's "wrong" answer. Stefan Ram's answer is the
>> intended one.
> Ian's answer has better justification. I'm going to support "banana".
Solving puzzles like this should come with a pleasing "ah!" moment which
usually comes from finding a simple rule or explanation. An arbitrary
answer is always possible, but it is rarely a rule, and although
arbitrary rules are also possible, they will rarely be simple. (On
average a rule will need at least as many symbols to be described as the
The trouble with this puzzle is that has at least two answers that are
simple rules and, to my mind, neither has a pleasing "ah!" associated
 Obviously this is not formal but it could be made so by reference to