Eta-reduction is an important operation in the lambda calculus.
A step of eta-reduction may be performed by eta_conv M, where M
is a lambda abstraction of the following form: \v. (N v), i.e.,
a lambda abstraction whose body is an application of a term N to
the bound variable v. Moreover, v must not occur free in M.
If this proviso is met, an invocation eta_conv (\v. (N v)) is equal
If M is not of the specified form, or if v occurs free in N.
- eta_conv (Term `\n. PRE n`);
> val it = `PRE` : term
Eta-reduction embodies the principle of extensionality, which is
basic to the HOL logic.