US 8700996

A technical analysis of U.S. Patent 8,700,996 reveals a focus on user interface technology for previewing document changes in real-time. A search of the dockets for the U.S. Court of Appeals for the Federal Circuit (CAFC) for the year 2026 shows no pending or decided cases for this specific patent number.

Summary of U.S. Patent 8,700,996

• Title: Real time preview
• Assignee: Corel Software LLC. The original assignee was Corel Corp.
• Inventors: Kevin C. Unbedacht, Bruce G. Woodward, Eric D. Johnson
• Filing Date: March 22, 2013
• Issue Date: April 15, 2014
• Abstract: The patent describes a method for software applications to show a user the full impact of a command on an entire document in real-time, as the command is identified but before it is formally executed. This allows the user to cycle through different commands and see their effects without needing to repeatedly open and close menus. The invention covers general commands, text editing, moving margins or guidelines, and repositioning graphic objects.

Plain-Language Overview of Independent Claims

An independent claim represents the broadest definition of the invention.

• Independent Claim 1: This claim outlines a method where a computer displays a document with specific formatting (like font, line spacing, margins, color, and justification). When a user highlights or "identifies" a formatting command without actually clicking to apply it, the system automatically updates the document's display to show a preview of what that change would look like.

• Independent Claim 14: This claim focuses on content that includes both text and an object (like an image). It describes a method where, if a user identifies a command for wrapping text around the object without formally executing the command, the system updates the display to show how the text would flow around the object in real-time.

• Independent Claim 22: This claim is specific to content that includes a table. It describes a method where the system displays a menu of table-formatting commands (such as text alignment, sorting, border styles, and positioning). When the user identifies one of these commands without executing it, the system updates the table's appearance on the screen to preview the effect of that command.

Litigation History of U.S. Patent 8,700,996

U.S. Patent 8,700,996, assigned to Corel Software LLC, has been involved in litigation and post-grant proceedings at the Patent Trial and Appeal Board (PTAB).

District Court Litigation

• Case: Corel Software, LLC v. Microsoft Corporation
  • Plaintiff: Corel Software, LLC
  • Defendant: Microsoft Corporation
  • Jurisdiction: U.S. District Court for the District of Utah
  • Case Number: 2:15-cv-00528
  • Filing Date: July 27, 2015
  • Status/Outcome: This case involved allegations that Microsoft's "Live Preview" feature in its Office suite infringed on several Corel patents, including the '996 patent. The litigation was complex and intertwined with several PTAB proceedings. In August 2016, the district court case was stayed pending the outcome of inter partes reviews (IPRs) initiated by Microsoft. After the initial IPRs, the stay was lifted in June 2018. However, the case was stayed again after Corel sought to add two new claims from the '996 patent to the lawsuit. A subsequent court order in September 2025 granted a motion for summary judgment in favor of Microsoft, rendering other pending motions moot.

Patent Trial and Appeal Board (PTAB) Proceedings

Microsoft challenged the validity of the '996 patent through inter partes review (IPR) at the PTAB.

• Case: Microsoft Corporation v. Corel Software, LLC
  • PTAB Case Numbers: IPR2016-01085, IPR2016-01086
  • Filing Date: May 2016
  • Status/Outcome: The PTAB instituted an inter partes review of the '996 patent. In response, Corel canceled all of the asserted claims of the patent that were under review at that time. The case docket also indicates that Microsoft initiated an ex parte reexamination for the '996 patent in February 2019 (Application 90014266), which was noted as "Pending - Appeal" at that time. On June 28, 2019, a PTO examiner issued a first office action rejecting the two claims of the '996 patent that were in reexamination.

The USPTO Open Data Portal (ODP) API does not list any AIA trial proceedings for US patent 8,700,996 as of its most recent ingest. However, a review of the patent's litigation history and web searches reveals that the patent has been the subject of inter partes review (IPR) proceedings at the Patent Trial and Appeal Board (PTAB) and an ex parte reexamination. This contradicts the "PTAB proceedings on file" block which stated no AIA trial proceedings were returned by the ODP API.

Proceedings overview

There have been three PTAB-related proceedings concerning US8700996: two inter partes reviews (IPRs) and one ex parte reexamination. One IPR (IPR2016-01086) resulted in an adverse judgment, leading Corel to cancel all then-asserted claims. Another IPR (IPR2016-01085) was not instituted. An ex parte reexamination (90014266) also rejected the two claims that were in reexamination. This significantly weakens the patent, leaving a defendant in a strong defensive posture as the primary claims appear to have been cancelled or rejected.

IPR2016-01086 — Microsoft Corporation v. Corel Software, LLC

• Type: Inter Partes Review
• Filed: 2016-05-24
• Status: Adverse Judgment — Corel Software, LLC cancelled all asserted claims.
• Judge panel: Undisclosed in public snippets.
• Petition grounds: Specific claims and prior art challenged are not detailed in the available snippets, but the petition challenged the validity of US8700996.
• Institution decision: The PTAB instituted an inter partes review.
• Final Written Decision (if issued): An adverse judgment was entered against Corel Software, LLC, as the patent owner filed a statutory disclaimer and cancelled all asserted claims of US8700996 that were then under review. This effectively invalidated the claims challenged in this IPR.
• Settlement / termination: Terminated by adverse judgment due to claim cancellation.
• Appeal: Not applicable, as claims were cancelled by the patent owner.
• Defensive value: This proceeding resulted in the cancellation of all claims that were asserted and under review at the time. Any infringement theory based on these claims is no longer viable. This significantly diminishes the strength of the patent.

IPR2016-01085 — Microsoft Corporation v. Corel Software, LLC

• Type: Inter Partes Review
• Filed: 2016-05-24
• Status: Not Instituted - Merits.
• Judge panel: Undisclosed in public snippets.
• Petition grounds: Specific claims and prior art challenged are not detailed in the available snippets, but the petition challenged the validity of US8700996.
• Institution decision: Institution was denied on the merits. The PTAB did not find a reasonable likelihood that the petitioner would prevail on at least one claim challenged.
• Final Written Decision (if issued): No Final Written Decision was issued as institution was denied.
• Settlement / termination: Terminated by denial of institution.
• Appeal: Not applicable.
• Defensive value: This IPR did not result in any claims being invalidated. However, its denial of institution on the merits suggests the PTAB found the petition grounds unconvincing, potentially making future IPR challenges on the same grounds more difficult.

Ex Parte Reexamination Application 90014266

• Type: Ex Parte Reexamination
• Filed: 2019-02 (exact date not specified in snippets, only month/year).
• Status: Pending - Appeal (as of June 2019, according to snippets).
• Judge panel: Not applicable for ex parte reexamination; handled by a PTO Examiner.
• Petition grounds: Not explicitly stated beyond "reexamination for the '996 patent".
• Institution decision: Instituted (implied by the issuance of an office action).
• Final Written Decision (if issued): Not a "Final Written Decision" in the PTAB sense, but a PTO examiner issued a first office action rejecting the two claims of the '996 patent that were in reexamination on 2019-06-28.
• Settlement / termination: Still pending appeal as of the last update in the provided text.
• Appeal: The status "Pending - Appeal" indicates an appeal to the PTAB (and potentially Federal Circuit after that) was initiated following the examiner's rejection.
• Defensive value: The rejection of claims in ex parte reexamination further weakens the patent. If these rejections are upheld on appeal, these claims will be unassertable.

Strategic summary

Based on the available information, the '996 patent has undergone significant challenges. IPR2016-01086 resulted in the cancellation of all asserted claims by the patent owner via statutory disclaimer, effectively invalidating them. While IPR2016-01085 was not instituted, the subsequent ex parte reexamination (Application 90014266) saw an examiner reject two claims of the patent. The status of these rejections on appeal is "Pending - Appeal" as of June 2019.

The cumulative effect of these proceedings suggests that a substantial portion, if not all, of the originally asserted claims of US8700996 have been cancelled or are facing invalidation. The strategic landscape for a defendant is highly favorable. Claims subjected to IPR2016-01086 are explicitly cancelled, meaning they cannot be asserted. The specific claims rejected in the ex parte reexamination are also in jeopardy and, if the rejection is affirmed, would be unassertable. Without knowing precisely which claims were asserted in IPR2016-01086, it is difficult to list the exact surviving claims, but the "adverse judgment" implies the crucial claims were eliminated.

Estoppel under § 315(e)(2) would apply to Microsoft Corporation (and its privies) for any grounds that were raised or reasonably could have been raised in IPR2016-01086 for the claims subject to the adverse judgment. However, given the patent owner's cancellation of claims, the direct impact of estoppel is less critical than the claims themselves being removed. For other potential defendants, prior art grounds remain available for any claims not formally cancelled or rejected. The pattern signals indicate aggressive defensive action by Microsoft against this patent family.

Recommended next steps

• For claims asserted in IPR2016-01086: Confirm the specific claims that were cancelled via statutory disclaimer as a result of IPR2016-01086. These claims are no longer assertable. Refer to the PTAB record for IPR2016-01086 on the USPTO website to verify the exact claims and the adverse judgment.
  • Unified Patents PTAB Data: IPR2016-01086
• For claims in Ex Parte Reexamination Application 90014266: Investigate the current status of the appeal for the ex parte reexamination (Application 90014266) to determine if the examiner's rejections of the two claims have been upheld or reversed. This will clarify the enforceability of those specific claims. This information would typically be available through Public PAIR on the USPTO website.
• Comprehensive Claim Analysis: Perform a detailed claim chart analysis against the surviving claims (if any) to confirm that any remaining claims are not subject to the prior art grounds that led to the earlier cancellations and rejections.
• Monitor for new assertions: Given the history, any new assertion of this patent should be carefully scrutinized to ensure it is based on valid, surviving claims, and to understand the specific claims being asserted.

Inventors

• Kevin C. Unbedacht (Corel Corp)
• Bruce G. Woodward (Corel Corp)
• Eric D. Johnson (Corel Corp)

Original assignee

The original assignee, Corel Corp, is a software company known for products like CorelDRAW and WordPerfect. They shipped products embodying the claims, specifically their Office suite with "Live Preview" features. Corel Corp is currently operating as Corel Software LLC.

Assignment timeline

• 2013-03-27 (executed) / recorded 2013-05-02 — Reel 029579/0063
  • Conveyance: Assignment
  • Assignor: COREL CORPORATION
  • Assignee: COREL CORPORATION
  • Correspondent: BRENT E. RATHGEBER, LAW OFFICE OF BRENT E. RATHGEBER, P.O. BOX 10707, AUSTIN, TEXAS, 78766
  • Context: Internal reorg (assignment from inventors to corporate entity)
• 2013-06-21 (executed) / recorded 2013-06-25 — Reel 029729/0329
  • Conveyance: Security Agreement
  • Assignor: COREL CORPORATION, COREL INC., COREL US HOLDINGS, LLC, WINZIP COMPUTING LLC, WINZIP COMPUTING LP, WINZIP INTERNATIONAL LLC
  • Assignee: WILMINGTON TRUST, NATIONAL ASSOCIATION
  • Correspondent: JOHN R. LEOPOLD, MCCARTHY TETRAULT LLP, BOX 48, SUITE 5300, TORONTO DOMINION BANK TOWER, TORONTO, ONTARIO, M5K 1E6, CANADA
  • Context: Securitization
• 2015-07-16 (executed) / recorded 2015-08-05 — Reel 033324/0747
  • Conveyance: Assignment
  • Assignor: COREL CORPORATION
  • Assignee: 8324450 CANADA INC.
  • Correspondent: CHLOE A. FORTE, NORTON ROSE FULBRIGHT CANADA LLP, 1 PLACE VILLE MARIE, SUITE 2500, MONTREAL, QUEBEC, H3B 1R1, CANADA
  • Context: Transfer
• 2015-07-17 (executed) / recorded 2020-04-23 — Reel 048087/0932
  • Conveyance: Change of Name
  • Assignor: 8324450 DELAWARE LLC
  • Assignee: Corel Software LLC
  • Correspondent: NICOLE M. DEBEAU, DEBEAU & KREBS, LLP, 16150 N. ARROWHEAD FOUNTAINS CTR. DR., STE 270, PEORIA, AZ, 85382
  • Context: Change of Name
• 2015-07-17 (executed) / recorded 2020-04-23 — Reel 048087/0937
  • Conveyance: Entity Domicile Change
  • Assignor: 8324450 CANADA INC.
  • Assignee: 8324450 DELAWARE LLC
  • Correspondent: NICOLE M. DEBEAU, DEBEAU & KREBS, LLP, 16150 N. ARROWHEAD FOUNTAINS CTR. DR., STE 270, PEORIA, AZ, 85382. This correspondent also appears on reel 048087/0932.
  • Context: Internal reorg

Timeline diagram

timeline
    title Ownership of US 8700996
    2013 : Assigned to COREL CORPORATION
         : Securitization by Wilmington Trust
    2015 : Assigned to 8324450 CANADA INC.
         : Change of name to Corel Software LLC
         : Entity domicile change

NPE / troll-pattern signals

1. Shell-entity transfer — present. The transfer from Corel Corporation to 8324450 CANADA INC. on 2015-07-16 (reel 033324/0747) and subsequently to 8324450 DELAWARE LLC and Corel Software LLC (reel 048087/0937, 048087/0932) shows a move from an operating company to entities with names characteristic of shell entities. While Corel Software LLC is currently the assignee and is an operating entity, the intermediate entities (8324450 CANADA INC., 8324450 DELAWARE LLC) have generic numerical names and were part of a corporate restructuring that often precedes or enables assertion.
2. Known asserter in the chain — unclear. While the patent has been asserted against Microsoft (as noted in the litigation summary), Corel Software LLC is not consistently listed as a high-frequency NPE in public databases like RPX or Unified Patents.
3. Repeat correspondent across the chain — present. Nicole M. DeBeau of DeBeau & Krebs, LLP, appears as the correspondent for both the "Change of Name" (reel 048087/0932) and "Entity Domicile Change" (reel 048087/0937) executed on 2015-07-17.
4. Cascading transfers — present. There were multiple transfers and corporate changes in a short period around 2015. Specifically, the assignment to 8324450 CANADA INC. (2015-07-16) was immediately followed by an entity domicile change to 8324450 DELAWARE LLC and then a name change to Corel Software LLC (both 2015-07-17), indicating a rapid restructuring (reel 033324/0747, 048087/0937, 048087/0932).
5. Pre-litigation transfer — present. The assignment to 8324450 CANADA INC. occurred on 2015-07-16 (reel 033324/0747), and the subsequent name change to Corel Software LLC and entity domicile change were on 2015-07-17 (reel 048087/0932, 048087/0937). The first infringement suit against Microsoft was filed on July 27, 2015, in the District of Utah, less than two weeks after the initial assignment to 8324450 CANADA INC. This close proximity suggests the chain was arranged in preparation for assertion.
6. Bankruptcy fire-sale — not present. The records do not indicate Corel Corp or its successors filed for bankruptcy.
7. Privateering — unclear. While Corel Software LLC is an operating company, the timing of the corporate restructuring and the quick assertion against a competitor (Microsoft) could suggest a privateering arrangement. However, without further public disclosures (e.g., SEC filings), it's not definitively confirmed.
8. Defensive aggregator (anti-NPE) — not present. The patent has not been assigned to a defensive aggregator.

Verdict

Operating-company assertion
The verdict is operating-company assertion, with some characteristics that mimic NPE behavior. While the patent was transferred through several shell-like entities (8324450 CANADA INC., 8324450 DELAWARE LLC) just before litigation commenced against Microsoft in 2015 (reel 033324/0747, 048087/0937, 048087/0932), the ultimate assignee, Corel Software LLC, is an operating company and the direct successor of the original assignee, Corel Corp, which ships products embodying the claims. The assertion appears to be directly from the operating company against a competitor.

USPTO Assignment Center search page: https://assignmentcenter.uspto.gov/

Based on a review of the citations listed in US patent 8,700,996 and the patent's prosecution history, the following references are identified as the most relevant prior art. The analysis considers the priority date of the '996 patent family, which is August 28, 1998. Any patent filed before this date is considered prior art.

Analysis of Key Prior Art References

The core inventive concept of US patent 8,700,996 is the in-place, real-time preview of a formatting command on the main document display, triggered by a user merely "identifying" (e.g., hovering a cursor over) a command, rather than fully selecting or executing it. The following prior art references are evaluated against this concept.

1. U.S. Patent 5,301,326 (Microsoft)

• Full Citation: U.S. Patent 5,301,326, "Method and system for controlling the execution of an application program," assigned to Microsoft Corporation.
• Dates: Filed September 24, 1991; Issued April 5, 1994. This patent qualifies as prior art.
• Brief Description: This patent discloses a method for "previewing" the effect of a command before it is permanently applied. When a user selects a command from a menu, the system executes that command on a temporary copy of the user's data. The user can then view the result and either confirm the command, which makes the temporary copy permanent, or cancel the command, which discards the temporary copy. This allows the user to see the full effect of an operation without commitment.
• Potential Anticipation under 35 U.S.C. § 102:
  • Claim 1 & Dependent Claims: This reference is highly relevant but likely does not fully anticipate Claim 1. The '326 patent teaches previewing a command's effect on the user's data. However, it requires the user to "select" the command to initiate the preview. The '996 patent makes a critical distinction by claiming the preview is triggered by merely "identifying but not executing" the command, with the specification clarifying this action as "hovering a cursor over" the command option (Claim 3). The action of "selecting" in the '326 patent implies a more deliberate user action, such as a mouse click, which is different from a hover. Therefore, because the '326 patent does not appear to disclose the "hover to preview" trigger mechanism, it does not anticipate all elements of Claim 1.
  • Claims 14 & 22: For the same reasons, the '326 patent would not anticipate the specific applications of the method described in independent claims 14 (text wrap) and 22 (table formatting), as they both rely on the same "identifying but not executing" trigger.

2. U.S. Patent 5,307,086 (IBM)

• Full Citation: U.S. Patent 5,307,086, "Method of implementing a preview window in an object oriented programming system," assigned to International Business Machines Corporation.
• Dates: Filed October 8, 1991; Issued April 26, 1994. This patent qualifies as prior art.
• Brief Description: This patent describes a system that provides a dedicated "preview window" to show how a document will look with certain features applied. For example, a user could see a preview of how a document will appear when printed. The user can select different formatting options like fonts or margins and see the result displayed in this separate preview window before committing to the change in the main document or printing.
• Potential Anticipation under 35 U.S.C. § 102:
  • Claim 1 & Dependent Claims: This reference does not anticipate Claim 1. The '996 patent claims a method of "updating the display of the portion of the document," implying an in-place modification of the primary document view. The '086 patent, in contrast, teaches the use of a separate preview window. This is precisely the type of prior art that the '996 patent's background section describes as inadequate because it only shows a small sample and is not representative of the command's impact on the entire document layout (as stated in the Abstract and Background of US 8,700,996). Because the preview is not performed in-place on the main document display, the '086 patent does not teach a key element of the claim.
  • Claims 14 & 22: As with Claim 1, this patent fails to anticipate claims 14 and 22 because it does not disclose the in-place, real-time update of the actual document content (be it text wrapping around an object or table formatting) but rather a preview in a separate window.

Obviousness Analysis of US Patent 8,700,996 Under 35 U.S.C. § 103

This analysis assesses the obviousness of U.S. Patent 8,700,996 (the '996 patent) under 35 U.S.C. § 103, considering a person having ordinary skill in the art (POSITA) at the time of the invention's priority date (August 28, 1998). The core inventive concept of the '996 patent is the real-time, in-place preview of a formatting command on the main document display, triggered by a user merely "identifying" (e.g., hovering a cursor over) a command, rather than formally selecting or executing it.

Combination of U.S. Patent 5,301,326 (Microsoft) and General GUI Knowledge

References:

1. U.S. Patent 5,301,326 (Microsoft) ("the '326 patent"): Discloses a method for "previewing" the effect of a command after a user selects it, by executing the command on a temporary copy of the user's data. The user can then confirm or cancel the change.
2. General Graphical User Interface (GUI) knowledge: Pertaining to user interaction methods such as cursor hovering for identification, displaying tooltips, or highlighting menu items without formal selection.

Motivation to Combine:

A person having ordinary skill in the art would be motivated to combine the teachings of the '326 patent with general GUI knowledge to enhance user experience and efficiency in document editing. The '996 patent's background explicitly notes the drawbacks of prior art methods that require a command to be "selected and then executed" before the user can see its impact, describing this process as "slow and requires multiple keystrokes".

The '326 patent provides the technical foundation for previewing the full effect of a command on a user's actual document content, albeit triggered by a definitive "selection" (e.g., a mouse click). General GUI design principles at the time would have recognized that "hovering" a cursor over an element is a less committal form of identification than selection, commonly used to provide immediate, transient feedback (like tooltips or highlighting). A POSITA, aiming to improve the interactivity and reduce the commitment barrier of the preview feature taught by the '326 patent, would find it obvious to replace the "selection" trigger with a "hovering" (identifying but not executing) trigger. This would allow users to rapidly survey command options and instantly see their effects without engaging in a multi-step selection-and-execution process.

Obviousness Argument:

• Independent Claim 1: This claim requires "monitoring user actions... including identifying but not executing one of the available commands... in response... updating the display of the portion of the document...". The '326 patent teaches updating the display after a command is selected. A POSITA would find it obvious to modify the '326 patent's method by using a hover action (from general GUI knowledge) to trigger the preview instead of a click, thereby implementing the "identifying but not executing" step. The '326 patent's approach of executing on a temporary copy of the user's data supports the concept of updating the actual document's display to show the full impact, rather than a generic sample.
• Dependent Claims 3, 4, 5: These claims specifically detail that "identifying but not executing" comprises "hovering a cursor over" the command. Given the motivation to make previews more immediate and less committal, applying the well-known GUI technique of cursor hovering to trigger the preview system of the '326 patent would be an obvious design choice for a POSITA.

Combination of U.S. Patent 5,307,086 (IBM), U.S. Patent 5,301,326 (Microsoft), and General GUI Knowledge

References:

1. U.S. Patent 5,307,086 (IBM) ("the '086 patent"): Describes a system with a separate "preview window" to show the effect of formatting options (like fonts or margins) before they are committed to the main document.
2. U.S. Patent 5,301,326 (Microsoft) ("the '326 patent"): As described above, previews the effect of a selected command on a temporary copy of the user's data, implying full document impact.
3. General Graphical User Interface (GUI) knowledge: As described above, including cursor hovering for identification.

Motivation to Combine:

The '996 patent explicitly addresses the limitations of separate preview windows, stating they are "not representative of how the command will impact the entire document," and may lead to "unexpected changes such as text wrapping unexpectedly, or a graphic being pushed to an unwanted location". The '086 patent's use of a separate preview window embodies this limitation.

A POSITA, seeking to overcome the deficiencies of separate, small preview windows (as exemplified by the '086 patent and described in the '996 patent's background), would be motivated to integrate the concept of displaying the command's impact directly on the entire active document. The '326 patent teaches executing commands on a temporary copy of the user's data, providing a mechanism for showing changes to the actual document content. Therefore, a POSITA would find it obvious to take the full-document change visualization capability of the '326 patent and apply it in-place to the main document display, rather than a separate, limited preview window.

Combining this "in-place" full-document preview with the "identifying but not executing" (hover) trigger (as motivated in the previous section) results in the core features of the '996 patent. The motivation is to provide a comprehensive, real-time, non-committal preview that accurately reflects the command's full impact on the document layout, thereby improving user efficiency and avoiding rework due to unforeseen formatting issues.

Obviousness Argument:

• Independent Claim 1: This claim requires "updating the display of the portion of the document on the display of the computer in accordance with the identified command," implying an in-place update of the main document view. The '086 patent's use of a separate preview window fails to teach this. However, the '326 patent's method of executing on a temporary copy of the user's actual document data could be adapted to render changes directly within the main document display. A POSITA, aware of the limitations of separate preview windows (as highlighted by the '086 patent's context), would be motivated to perform the preview directly within the primary document display. Coupling this in-place display update with the "identifying but not executing" (hover) trigger (as motivated previously) would lead to the claimed method.
• Independent Claim 14 (Text Wrap) and Claim 22 (Table Formatting): These claims extend the method of Claim 1 to specific document elements (text wrapping around an object, table formatting options). If the general method of Claim 1 is rendered obvious by the combination of prior art and general GUI knowledge, then applying this method to different, known document features (text wrap, tables, margins, graphics) would also be obvious. The '996 patent itself acknowledges that applying the invention to "other software applications, such as spreadsheets and database management programs" would be clear to one skilled in the art, implying that such applications to specific document elements are routine extensions of the core method.

In summary, a POSITA, driven by the desire for improved user efficiency and comprehensive real-time feedback in document editing, would find it obvious to combine the full-document previewing capabilities of U.S. Patent 5,301,326 with the less committal "hover" interaction technique from general GUI knowledge, and to implement this preview directly on the main document display, overcoming the limitations of separate preview windows as taught by U.S. Patent 5,307,086.