Please explain the basic rules of offer, including reference to the following (with relevant case and statute law where appropriate):

An offer is a statement of willingness to be bound

by the terms of the offer

It must be distinguished from 'invitation to treat'

and a mere statement of price

An offer must be communicated to the offeree -

but can be made to the whole world

Its terms must be certain

An offer can be withdrawn any time up to

acceptance - can be by a reliable third party

A unilateral offer only requires performance

Offer ends on acceptance, proper withdrawal, lapse

of time, death of one of the parties