=/ 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 door: a core carrying a sample, with many named arms.

~(arm door value) sets the sample, then pulls that arm.

a door is a gate with many named entry points.

=/  d
  |_  n=@
  ++  inc  (add n 1)
  --
~(inc d 4)

is 5.

$= wraps a mold with a face, naming the value it produces.

$=(x @) is the mold x=@.

%: calls a gate with several arguments, gathering them into one sample.

%:(add 2 3) is 5.

irregular forms:

(gate a b c) is %:(gate a b c)

mul multiplies two atoms.

(mul 3 4) is 12.