The U.S. Patent and Trademark Office (USPTO) issued guidance concerning “Examining Computer-Implemented Functional Claim Limitations for Compliance With 35 U.S.C. 112”, 84 Fed. Reg. 57 (Jan. 7, 2019) [hereinafter “2019 USPTO Guidance”]. The 2019 USPTO Guidance applies to all pending applications and issued patents as of January 7, 2019, and was issued on the same day that the USPTO released revised guidelines for evaluating patent subject matter eligibility under the statutory requirement of 35 U.S.C. §101. The 2019 USPTO Guidance points out that, in the context of Section 101, the U.S. Court of Appeals for the Federal Circuit has criticized improper functional claiming, but also states that one reason for issuing the 2019 USPTO Guidance was to emphasize that problems with functional claiming (i.e. when a claim is purely functional in nature rather than reciting with any specificity how the claimed function is achieved) can be effectively addressed under Section 112.
Means-plus-function claiming is permitted under 35 U.S.C. §112(f), or pre-AIA 35 U.S.C. 112, sixth paragraph, which states:
An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.
In Williamson v. Citrix Online, LLC, 792 F.3d 1339, 1349 (Fed. Cir. 2015) (en banc), which is discussed in the 2019 USPTO Guidance, the Federal Circuit overruled the “strong” presumption flowing from the absence of the term “means” set forth in Lighting World, Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1358 (Fed. Cir. 2004) [holding that “ ... the presumption flowing from the absence of the term “means” is a strong one that is not readily overcome”] and also overruled the requirement set forth in Flo Healthcare Solutions, LLC v. Kappos, 697 F.3d 1367, 1374 (Fed. Cir. 2012) [holding that “[w]hen the claim drafter has not signaled his intent to invoke § 112, ¶ 6 by using the term ‘means,’ we are unwilling to apply that provision without a showing that the limitation essentially is devoid of anything that can be construed as structure”, citing Masco Corp. v. United States, 303 F.3d 1316, 1327 (Fed. Cir. 2002)]. Rather, the Federal Circuit stated that “... [t]he standard is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure. In interpreting the claim element “distributed learning control module”, the Federal Circuit stated that “module” is a non-structural nonce word which is tantamount to “means” in the Section 112(6) analysis, that the prefix “distributed learning control” did not impart structure into the term “module”, and that “the written description fails to impart any structural significance to the term.” Since such claim element in Williamson failed to recite sufficiently definite structure, the presumption against means-plus function claiming was rebutted, and the claim element was interpreted under Section 112(6).
The 2019 USPTO Guidance (Part I) discusses the Williamson opinion and claim interpretation under 35 U.S.C. §112(f) (i.e. means-plus-function limitations), referring to the 3-prong analysis set forth in MPEP, §2181, subsection I, as to whether 35 U.S.C. §112(f) is to be applied to a claim limitation. Such 3-prong analysis includes evaluating (i) whether the limitation uses the term ‘‘means’’ (or ‘‘step’’) or a generic placeholder, (ii) whether the term is modified by functional language, and (iii) whether the term is modified by sufficient structure, material or acts for performing the function. If the Examiner determines that a claim includes a means-plus-function limitation, the Office Action should expressly state that the limitation is being construed under 35 U.S.C. §112(f) by consulting the specification to determine the corresponding structure, material, or act for performing the claimed function, and that to avoid such interpretation, applicant may (1) present a sufficient showing to establish that the claim limitation recites sufficient structure to perform the claimed function so as to avoid interpretation under 35 U.S.C. §112(f), or (2) amend the claim limitation in a way that avoids interpretation under 35 U.S.C. §112(f) (e.g., by reciting sufficient structure to perform the claimed function).
The 2019 USPTO Guidance (Part I) further states that when a means-plus-function limitation recites a specific computer function, such claim is indefinite under 35 U.S.C. §112(b) unless the specification discloses an algorithm for performing the recited specific computer function. The 2019 USPTO Guidance also refers to the holding of the Federal Circuit in In re Aoyama, 656 F.3d 1293,1297 (Fed. Cir. 2011) that reference in the specification to a general purpose computer, by itself, will not be sufficient; rather, the disclosed algorithm must be provided and when a computer is appropriately programmed to perform the disclosed algorithm, such computer becomes a special purpose computer having the required structure corresponding to the recited function. According to the 2019 USPTO Guidance, an algorithm is “a finite sequence of steps for solving a logical or mathematical problem or performing a task”, and such algorithm can be expressed in “... any understandable terms including as a mathematical formula, in prose, or as a flow chart, or in any other manner that provides sufficient structure.’’ Further, the requirement to disclose the algorithm cannot be avoided by arguing that one of ordinary skill in the art could write software to convert a general purpose computer to a special purpose computer to perform the claimed function. The algorithm must be disclosed such that the entire claimed function can be performed. For example, in Williamson, 792 F.3d at 1351–52, while the Federal Circuit determined that ‘‘distributed learning control module’’ is a means-plus function limitation that performs three specialized functions (i.e., ‘‘receiving,’’‘‘relaying,’’ and ‘‘coordinating’’), the Federal Circuit held that no algorithm was disclosed for the ‘coordinating function’, and therefore that the claims containing the ‘‘distributed learning control module’’ limitation are invalid for indefiniteness under 35 U.S.C. §112(b). The 2019 USPTO Guidance further explains that when a claim containing a computer-implemented means-plus-function claim limitation is found to be indefinite for failure to disclose sufficient corresponding structure in the specification (e.g., the computer and the algorithm) that performs the entire claimed function, it would also lack the required written description under 35 U.S.C. §112(a).
The 2019 USPTO Guidance (Part II) also addresses written description and enablement issues under 35 U.S.C. §112(a), as pertaining to examination of computer-implemented functional claim limitations. In order to determine whether the written description requirement is satisfied, the Examiner must compare the scope of the claims with the scope of the application, to determine whether applicant has demonstrated possession of the claimed invention. The 2019 USPTO Guidance points out that for computer-implemented functional claims, determination of the sufficiency of the disclosure requires an inquiry into the sufficiency of both the disclosed hardware and the disclosed software, due to the interrelationship and interdependence of computer hardware and software, and that the specification must disclose the computer and the algorithm(s) that achieve the claimed function in sufficient detail such that one of ordinary skill in the art can reasonably conclude that the inventor possessed the claimed subject matter at the time of filing.
Part II also points out that to satisfy the enablement requirement of 35 U.S.C. §112(a), the specification must teach those skilled in the art how to make and use the full scope of the claimed invention without undue experimentation. Although the 2019 USPTO Guidance points out that, for the purposes of enablement, a specification need not disclose what is well known in the art, applicant cannot rely on the knowledge of one skilled in the art to supply information that is required to enable the novel aspect of the claimed invention, when the enabling knowledge is in fact not known in the art. The 2019 USPTO Guidance further points out that the fact that a specification need not disclose what is well known in the art, for the purposes of enablement, is of particular importance with respect to computer-implemented inventions due to the high level of skill in the art and the similarly high level of predictability in generating programs to achieve an intended result without undue experimentation.
In sum, in order to provide a sufficient disclosure for computer-implemented inventions in compliance with Section 112, it is critical that an algorithm for performing each claimed specific computer function be disclosed, regardless of whether or not the claim limitation is ultimately interpreted as a means-plus-function limitation.
 Williamson at 1349.
 Id. at 1349 (citing Greenberg, 91 F.3d at 1583 (Fed. Cir. 1996)).
 Id. at 1351.
 See Manual of Patent Examining Procedure (9th ed. Rev. 08.2017, Jan. 2018) (hereinafter “MPEP”), §2181, subsection I.
 Net MoneyIN, Inc. v. VeriSign, Inc., 545 F.3d 1359, 1367 (Fed. Cir. 2008).
 Microsoft Computer Dictionary (5th ed., 2002).
 Finisar Corp. v. DirecTV Grp., Inc., 523 F.3d 1323, 1340 (Fed. Cir. 2008) (internal citation omitted).
 See EON Corp. IP Holdings LLC v. AT&T Mobility LLC, 785 F.3d 616, 623 (Fed. Cir. 2015).
 Williamson at 1354.
 See MPEP § 2163.03, subsection VI.
 See MPEP § 2163, subsection II(A)(2); see also Reiffin v. Microsoft Corp., 214 F.3d 1342, 1345 (Fed. Cir. 2000).
 See Vasudevan Software, Inc. v. MicroStrategy, Inc., 782 F.3d 671, 683 (Fed. Cir. 2015).
 See MPEP § 2161.01, subsection III, and MPEP § 2164.08.