Index-Of Extension
Index
<<
>>
x⍳y
←→
(⊂⍤¯1⊢x) ⍳ ⊂⍤(¯1+⍴⍴x)⊢y
←→
(⊂[1↓⍳⍴⍴x]x) ⍳
⊂[(1-⍴⍴x)↑⍳⍴⍴y]y
generalization of matiota
{(↓⍺)⍳↓⍵}