⍛
f⍛g Y is (f Y)g Y. Useful for computing a mask then filtering.
f⍛g Y
(f Y)g Y
3∘<⍛/2 7 1 8 ⍝ 7 8
X f⍛g Y is (f X)g Y.
X f⍛g Y
(f X)g Y
3 -⍛+ 10 ⍝ 7