⍢ Under r←[x]({Fn}⍢G)y

G is a structural monadic function, i.e. a function that only reorders the argument without changing or depending on the elements' values, except for their ordering. r is the result of applying G, calling [x∘]F, or n⍨ on the reordered elements and then undo the reordering. If the result of F/n⍨ is scalar, the result is repeated for all substituted elements of the result.

Functions supported as G

• ↑ Take
• ↓ Drop
• ⊖ Reverse
• ⊖ Rotate
• ⍉ Transpose
• ⍴ Reshape
• ϼ Rerank
• , Ravel
• ∧ Promote
• ∨ Demote
• ⌷ Index
• ⊇ From
• ⊃ First (if y is simple)
• ⊇ Last (if y is simple)
• ⌿ Replicate
• ⊴ Sort Up
• ⊵ Sort Down (not stable)
• All combinations of these functions
• These function on any ⍤ At Rank
• All dfns which are structural, as defined above