Beside

, Compose or After is a primitive operator. It shares the glyph Jot with Bind. Called dyadically with function operands  and , it uses   monadically to pre-processes the right argument before applying   to the given left argument and pre-processed right argument. Called monadically with operands  and , it applies   to the result of applying   to the argument.

In usage,  is equivalent to , and   is equivalent to. Thus, beside can be defined as the dop.

Examples
When used monadically,  behaves the same as an atop:

When used dyadically,  forms a dyadic hook:

When used monadically with Commute,  forms a monadic hook:

Lessons

 * APL Cultivation

Documentation

 * Dyalog