The outer variable isn't set until the block finishes, so it's not shadowed (it does look as if it is, and I toyed with calling it something different, but it's genuinely the same concept).

You're quite right, 72 is redundant. It's my safety mechanism - whenever I use `inject` with hashes, I forget to use it. In the case of `concat` since you get the array, you can forgo it. It's just habit these days.