According to the footnote A in the book, it should be the first letter of the arrangement, but the English word for "arrangement" in mathematics is Permutation.

I read the explanation in the dictionary that arrangement refers to the "arrangement" of anything in the general sense, and there are many other meaning; On the other hand, permutation has a special mathematical explanation: "One"

tidy/neat

appoint

about

this

element

about

a

Set "(an ordered arrangement of elements in a set). In addition, all the mathematical nouns containing "permutation" use permutation instead of permutation. Is this too inappropriate?

When I study computer, I must learn combinatorial mathematics. As a result, after two symbols appear here in class, I often use P and A at the same time, which makes it very confusing. I will unconsciously write P on the math paper, or I will unconsciously make a combination formula when I write A to calculate. ...