Where two or more related inventions are claimed, the principal question to be determined in connection with a requirement to restrict or a rejection on the ground of double patenting is whether or not the inventions as claimed are distinct. If they are distinct, restriction may be proper. If they are not distinct, restriction is never proper. If nondistinct inventions are claimed in separate applications or patents, double patenting must be held, except where the additional applications were filed consonant with a requirement to restrict.
Various pairs of related inventions are noted in the following sections. In applications claiming inventions in different statutory categories, only one-way distinctness is generally needed to support a restriction requirement. See MPEP § 806.05(c) (combination and subcombination) and § 806.05(j) (related products or related processes) for examples of when a two-way test is required for distinctness. Related inventions in the same statutory class are considered mutually exclusive, or not overlapping in scope, if a first invention would not infringe a second invention, and the second invention would not infringe the first invention