Method Claim with Specific Preamble Structure Not Indefinite

Citing William Shakeseare in Microprocessor Enhancement Corp. v. Texas Instruments Inc. (April 1, 2008), the the U.S. Court of Appeals for the Federal Circuit held that a method claim was not invalid for indefiniteness even though it included specific structural features in the preamble of the form

1. A method of executing instructions in a pipelined processor comprising:
[extensive structural limitations of the pipelined processor];
the method further comprising:
[method steps implemented in the pipelined processor].

because it did not impermissibly claim mixed classes of subject matter. According to the opinion by Circuit Judge Gajarsa,

Although this seeming preamble within a preamble structure is unconventional,
its effect on the definiteness of claim 1 lacks the conclusiveness with which
King Claudius’s guilt is established by his reaction to Hamlet’s play within a
play. See William Shakespeare, Hamlet act 3, sc. 2. Method claim preambles often
recite the physical structures of a system in which the claimed method is
practiced, and claim 1 is no different. The conclusion of IPXL Holdings was
based on the lack of clarity as to when the mixed subject matter claim would be
infringed. 430 F.3d at 1384 ("[I]t is unclear whether infringement of claim 25
occurs when one creates a system that allows the user to [practice the claimed
method step], or whether infringement occurs when the user actually [practices
the method step]."). There is no similar ambiguity in claim 1 of the ’593
patent. Direct infringement of claim 1 is clearly limited to practicing the
claimed method in a pipelined processor possessing the requisite structure.

As the Bard of Avon himself might have quipped "Why may not that be the skull of a lawyer? Where be his quiddities now, his quillets, his cases, his tenures, and his tricks?"