1.NounOne of the three rewrite rules of lambda calculus, which expresses a sort of tautology about function application. The rule says that a lambda abstraction of the form
(
λ
x
.
(
f
x
)
)
{\displaystyle (\lambda x.(fx))}
may be rewritten as simply
f
{\displaystyle f}
, provided that x does not occur freely in f (considered by itself).