head normal form การใช้

• Head normal forms are the terms of the following shape:
• However, the converse is true : any normal form is also a head normal form.
• In fact, the normal forms are exactly the head normal forms in which the subterms M _ j are themselves normal forms.
• More generally, a "'head normal form "'is a term that do not contain a beta redex in head position, " ie . " that cannot be further reduced by a head reduction.
• Normal-order reduction is complete, in the sense that if a term has a head normal form, then normal order reduction will eventually reach it; by the syntactic description of normal forms above, this entails the same statement for a  fully normal form ( this is the standardization theorem ).