A expression has the form
E := V | (E1 E2) | (V.E1)
where V denotes variables
(E1 E2) is an application
and (V.E1) is an abstraction.
examples:
(v.v)
(v.(v (x y)))
Most books use a notation with implicit left associativity. Thus
(E1 E2 E3) means ((E1 E2) E3)
(v.E1 E2) means (
v.(E1 E2))