Many national and regional patent offices provide procedures for reconsidering whether or not a given patent is valid after grant. Under the European Patent Convention, any person can file an opposition provided they act promptly after grant of the patent. In the United States, members of the public can initiate reexamination proceedings. Japan provides similar options as well. In India, the Patent Act provides for a dual opposition system i.e. pre-grant opposition as well as post grant opposition. While a pre-grant opposition may be filed by any person, the post grant opposition may only be filed by a person interested in the field of invention.