⍝ I'm sure that GLS knows this, but ∆ (delta) is a valid APL symbol (APL\SV) that looks like one of the primitives but may be user-defined. As I recall (it's b

⍝ I'm sure that GLS knows this, but ∆ (delta) is a valid APL symbol (APL\SV) that looks like one of the primitives but may be user-defined. As I recall (it's been a while since I sat in front of a Selectric with an appropriate typeball or a real 3270 with an overflowing ashtray sitting next to it), it's unfortunately the only one, so it was understandably handwaved away.