You’ve got it backwards
&.
The under conjunction, denoted by &. , is like composition. The expression (f &. g) x is defined to mean g^:_1 f g x that is, g is applied to the argument, then f is applied to this result, and finally the verb obverse to g is applied (the obverse is usually the inverse). For example, to perform a sum scan from right to left, sum=.+/ sumscan=.sum\ sumscan 1 2 3 4 1 3 6 10 backwards=.&.|. sumscan backwards 1 2 3 4 10 9 7 4 |