=/ pins a named value (a face) into the subject for the lines below it.

name=value optionally declares the type.

=/(a 3 (add a a)) is 6.

|% makes a core: a battery of named arms, each written ++ name.

reach an arm back out with =< or arm:core.

=<  a
|%
++  a  5
--

is 5.

=< evaluates its head against its tail as subject.

=<(a b) is =>(b a), and =<(a [a=5]) is 5.

irregular forms:

arm:core is =<(arm core)