Mathematica 降值 Lhs [英] Mathematica Downvalue Lhs

问题描述

有谁知道 Mathematica 中是否有一个内置函数来获取降值规则的 lhs(没有任何持有)?我知道如何编写代码来做到这一点，但对于内置的来说它似乎足够基本

Does anybody know if there is a built-in function in Mathematica for getting the lhs of downvalue rules (without any holding)? I know how to write the code to do it, but it seems basic enough for a built-in

例如:

a[1]=2;
a[2]=3;

BuiltInIDoNotKnowOf[a] 返回 {1,2}

推荐答案

这似乎有效；不过不确定它有多大用处:

This seems to work; not sure how useful it is, though:

a[1] = 2
a[2] = 3
a[3] = 5
a[6] = 8
Part[DownValues[a], All, 1, 1, 1]

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