*Classic Edition:* the symbol ⍤ is not available in Classic Edition, and the Atop operator is instead represented by ⎕U2364.

f can be any monadic function. Y can be any array that is suitable as the right argument to function g with the result of g being appropriate to function f.

If X is omitted, g must be a monadic function. If X is specified, g must be a dyadic function and X can be any array that is suitable as the left argument to function g.

The derived function is equivalent to fgY or fXgY and need not return a result.

The Atop operator allows functions to be glued together to build up more complex functions. For further information, see Function Composition.

#### Examples:

-⍤÷ 4 ⍝ ( f⍤g y) ≡ f g y ¯0.25 12 -⍤÷ 4 ⍝ (x f⍤g y) ≡ (f x g y) ¯3 3 1 4 1 5 ~⍤∊ 1 2 3 0 0 1 0 1