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> I love the typesetting of the math in these old papers

I agree except that the first thing the paper does is define "1" to be a function that "produces a vector of the first N integers". Highly confusing. It turns out that symbol isn't a "1" and rather is a weird squiggle that unfortunately looks like one.

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It should be the Greek letter iota (i.e. I from indices). Besides iota, APL uses frequently the Greek letter rho (i.e. R from rank; rho applied once gives a vector with the array dimensions and applied twice it gives the dimension of the rho vector, i.e. the tensor rank of the array).

Interesting. I don't think "ι" looks like "1" at all.

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