How long do you have to rewrite every such expression with pencil on paper, before you start to be able to apprehend these things directly? I'm not trying to bring this down, clearly it's very concise, just curious what the learning curve is with that.
The winner of this year's APL Problem Competition only started learning APL a year ago. And lots of people never handwrite APL, though many do, but not to understand — to simply do certain maths in a better way.
⍳ is range 0…n–1
÷ is reciprocal of everything to its right
×/ is product of everything to its right
+/ is sum of everything to its right