Hello J,
Using J primitives, what are some nice algebraic identities you know of?
I recently acquired a copy of "At Play with J" and in the process of mulling
over chapter 7's permutation representations, I stumbled upon this nice one,
which I assume is already well known:
/: -: /:@/:@/:
which essentially embodies the fact that /: maps a permutation to its inverse,
so if y is a permutation of integers, then
y -: /: /: y
The extra layer of /: comes from the fact that /: is capable of mapping
arbitrary lists to permutations.
Anyway, this got me excited about the idea of manipulating J expressions
algebraically. I would love to hear about any pearls you may know about.
Cheers!
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