K Number
K203040
Device Name
TSolution One Total Knee Application
Date Cleared
2020-11-13

(38 days)

Product Code
Regulation Number
882.4560
AI/MLSaMDIVD (In Vitro Diagnostic)TherapeuticDiagnosticis PCCP Authorized
Intended Use
The TSolution One® Total Knee Application is intended for use as a device that uses diagnostic images of the patient acquired specifically to assist the physician with preoperative planning and to provide orientation and reference information during intraoperative procedures. The robotic surgical tool, under the direction of the surgeon, precisely implements the presurgical software plan. The preoperative planning software and robotic surgical tool are used as an alternative to manual planning and resecting techniques for the distal femur and proximal tibia preparation in primary total knee arthroplasty (TKA). The TSolution One® Total Knee Application is indicated for orthopedic procedures in which resecting techniques used for the distal femur and proximal tibia may be considered to be as safe and effective and where references to rigid anatomical structures may be made. The TSolution One® Total Knee Application is also intended to assist the surgeon in determining reference alignment axes in relation to anatomical and instrumentation structures during stereotactic orthopedic surgical procedures. The TSolution One® Total Knee Application facilitates accurate positioning of TKA implants, relative to these alignment axes. The TSolution One® Total Knee Application is compatible with the following Knee Implant Systems: - . Zimmer Persona™ Knee System - . Corin Unity Knee System - . Aesculap Columbus Knee System - . DJO Surgical® EMPOWR 3D Knee® System - . United U2 Knee System
Device Description
Like its predicate, the TSolution One® Total Knee Application is a three-dimensional, graphical, preoperative planning workstation and implementation tool for treatment of patients who require total joint arthroplasty. The device is intended as an alternative to manual template planning and preparation of the bone with patients requiring primary total knee arthroplasty (TKA). The TSolution One® Total Knee Application consists of TPLAN and TCAT. TPLAN is a three-dimensional (3D) preoperative planning workstation that aids a surgeon in planning the position and orientation of the implant components relative to 3D models of the patient's anatomy. TCAT consists of an electromechanical arm, an arm base including control electronics and computer, a display monitor, operating software, pendant control, and tools and accessories, for the implementation of the preoperative plan. TCAT and TPLAN when used according to the instructions for use, make submillimeter precision bone preparation possible before and during TKA surgical procedures.
More Information

No
The summary describes a robotic surgical system for total knee arthroplasty that uses preoperative planning software and a robotic arm for precise bone preparation. It focuses on 3D planning, electromechanical components, and accuracy testing. There is no mention of AI, ML, or related concepts like training data, test data, or specific algorithms associated with learning or intelligent decision-making. The system appears to execute a pre-defined plan rather than adapt or learn.

No
This device is a surgical planning and implementation tool for total knee arthroplasty, assisting surgeons in bone preparation and implant positioning. It is not directly therapeutic but rather a tool used during a therapeutic procedure.

Yes

The intended use states that the device uses diagnostic images "specifically to assist the physician with preoperative planning". While it also assists with intraoperative procedures, its role in processing diagnostic images for planning purposes classifies it as a diagnostic device.

No

The device description explicitly states that the TSolution One® Total Knee Application consists of both TPLAN (preoperative planning software) and TCAT, which includes an electromechanical arm, arm base, control electronics, computer, display monitor, operating software, pendant control, and tools and accessories. This clearly indicates the presence of significant hardware components in addition to the software.

Based on the provided information, the TSolution One® Total Knee Application is not an In Vitro Diagnostic (IVD) device.

Here's why:

  • Intended Use: The intended use clearly states that the device is for preoperative planning and intraoperative guidance during total knee arthroplasty. It uses diagnostic images (CT scans) to assist the physician in planning and then a robotic tool to implement that plan during surgery.
  • Device Description: The description reinforces this by detailing a planning workstation and a robotic arm for bone preparation.
  • Lack of IVD Characteristics: An IVD device is typically used to examine specimens (like blood, tissue, or urine) in vitro (outside the body) to provide information for diagnosis, monitoring, or screening. The TSolution One® operates in vivo (within the body) during surgery and uses images of the patient's anatomy, not biological specimens.

The device is a surgical planning and robotic assistance system, not a diagnostic test performed on biological samples.

N/A

Intended Use / Indications for Use

The TSolution One® Total Knee Application is intended for use as a device that uses diagnostic images of the patient acquired specifically to assist the physician with preoperative planning and to provide orientation and reference information during intraoperative procedures. The robotic surgical tool, under the direction of the surgeon, precisely implements the presurgical software plan.

The preoperative planning software and robotic surgical tool are used as an alternative to manual planning and resecting techniques for the distal femur and proximal tibia preparation in primary total knee arthroplasty (TKA).

The TSolution One® Total Knee Application is indicated for orthopedic procedures in which resecting techniques used for the distal femur and proximal tibia may be considered to be as safe and effective and where references to rigid anatomical structures may be made.

The TSolution One® Total Knee Application is also intended to assist the surgeon in determining reference alignment axes in relation to anatomical and instrumentation structures during stereotactic orthopedic surgical procedures. The TSolution One® Total Knee Application facilitates accurate positioning of TKA implants, relative to these alignment axes.

The TSolution One® Total Knee Application is compatible with the following Knee Implant Systems:

  • . Zimmer Persona™ Knee System
  • . Corin Unity Knee System
  • . Aesculap Columbus Knee System
  • . DJO Surgical® EMPOWR 3D Knee® System
  • . United U2 Knee System

Product codes

OLO

Device Description

Like its predicate, the TSolution One® Total Knee Application is a three-dimensional, graphical, preoperative planning workstation and implementation tool for treatment of patients who require total joint arthroplasty. The device is intended as an alternative to manual template planning and preparation of the bone with patients requiring primary total knee arthroplasty (TKA).

The TSolution One® Total Knee Application consists of TPLAN and TCAT. TPLAN is a three-dimensional (3D) preoperative planning workstation that aids a surgeon in planning the position and orientation of the implant components relative to 3D models of the patient's anatomy. TCAT consists of an electromechanical arm, an arm base including control electronics and computer, a display monitor, operating software, pendant control, and tools and accessories, for the implementation of the preoperative plan. TCAT and TPLAN when used according to the instructions for use, make submillimeter precision bone preparation possible before and during TKA surgical procedures.

Mentions image processing

Not Found

Mentions AI, DNN, or ML

Not Found

Input Imaging Modality

CT Scan

Anatomical Site

distal femur and proximal tibia

Indicated Patient Age Range

Not Found

Intended User / Care Setting

physician / surgical procedures

Description of the training set, sample size, data source, and annotation protocol

Not Found

Description of the test set, sample size, data source, and annotation protocol

Not Found

Summary of Performance Studies (study type, sample size, AUC, MRMC, standalone performance, key results)

Performance testing to verify the cutting accuracy of the subject device was conducted following similar test methods and acceptance criteria to those used for the predicate device. Electromagnetic Compatibility and Electrical Safety testing met the requirements of applicable IEC standards. Validation testing, with methods and acceptance criteria similar to that used for the predicate device, was conducted using simulated surgical testing in a cadaver model and all test criteria were met. Biocompatibility Testing performed according to the ISO 10993-1:2009 standard was completed on any new patient contacting materials. All of this testing demonstrated that the TSolution One® Total Knee Application met the test criteria and specifications of the predicate device.

  • Cutting Accuracy Verification: Passed
  • Cadaver Lab Validation Testing: Passed
  • Software Testing: Passed
  • Electromagnetic Compatibility and Electrical Safety: Passed
  • Biocompatibility Testing on Changed Materials: Passed

Key Metrics (Sensitivity, Specificity, PPV, NPV, etc.)

Not Found

Predicate Device(s)

K201255

Reference Device(s)

K191369

Predetermined Change Control Plan (PCCP) - All Relevant Information

Not Found

§ 882.4560 Stereotaxic instrument.

(a)
Identification. A stereotaxic instrument is a device consisting of a rigid frame with a calibrated guide mechanism for precisely positioning probes or other devices within a patient's brain, spinal cord, or other part of the nervous system.(b)
Classification. Class II (performance standards).

0

November 13, 2020

Image /page/0/Picture/1 description: The image shows the logo of the U.S. Food and Drug Administration (FDA). On the left is the Department of Health & Human Services logo. To the right of that is the FDA logo in blue, with the words "U.S. FOOD & DRUG" stacked on top of the word "ADMINISTRATION".

THINK Surgical, Inc. Meliha Mulalic Director, Regulatory Affairs and Quality Assurance 47201 Lakeview Blvd Fremont, California 94538

Re: K203040

Trade/Device Name: TSolution One Total Knee Application Regulation Number: 21 CFR 882.4560 Regulation Name: Stereotaxic Instrument Regulatory Class: Class II Product Code: OLO Dated: October 5, 2020 Received: October 6, 2020

Dear Meliha Mulalic:

We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database located at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal

1

statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801); medical device reporting of medical device-related adverse events) (21 CFR 803) for devices or postmarketing safety reporting (21 CFR 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reportingcombination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to https://www.fda.gov/medical-device-safety/medical-device-reportingmdr-how-report-medical-device-problems.

For comprehensive regulatory information about medical devices and radiation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medicaldevices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-device-advice-comprehensive-regulatoryassistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely,

Shumaya Ali, MPH Assistant Director DHT6C: Division of Restorative, Repair and Trauma Devices OHT6: Office of Orthopedic Devices Office of Product Evaluation and Quality Center for Devices and Radiological Health

Enclosure

2

Indications for Use

510(k) Number (if known) K203040

Device Name TSolution One® Total Knee Application

Indications for Use (Describe)

The TSolution One® Total Knee Application is intended for use as a device that uses diagnostic images of the patient acquired specifically to assist the physician with preoperative planning and to provide orientation and reference information during intraoperative procedures. The robotic surgical tool, under the direction of the surgeon, precisely implements the presurgical software plan.

The preoperative planning software and robotic surgical tool are used as an alternative to manual planning and resecting techniques for the distal femur and proximal tibia preparation in primary total knee arthroplasty (TKA).

The TSolution One® Total Knee Application is indicated for orthopedic procedures in which resecting techniques used for the distal femur and proximal tibia may be considered to be as safe and effective and where references to rigid anatomical structures may be made.

The TSolution One® Total Knee Application is also intended to assist the surgeon in determining reference alignment axes in relation to anatomical and instrumentation structures during stereotactic orthopedic surgical procedures. The TSolution One® Total Knee Application facilitates accurate positioning of TKA implants, relative to these alignment axes.

The TSolution One® Total Knee Application is compatible with the following Knee Implant Systems:

  • . Zimmer Persona™ Knee System
  • . Corin Unity Knee System
  • . Aesculap Columbus Knee System
  • . DJO Surgical® EMPOWR 3D Knee® System
  • . United U2 Knee System

Type of Use (Select one or both, as applicable)

X Prescription Use (Part 21 CFR 801 Subpart D)

Over-The-Counter Use (21 CFR 801 Subpart C)

CONTINUE ON A SEPARATE PAGE IF NEEDED.

This section applies only to requirements of the Paperwork Reduction Act of 1995.

DO NOT SEND YOUR COMPLETED FORM TO THE PRA STAFF EMAIL ADDRESS BELOW.

The burden time for this collection of information is estimated to average 79 hours per response, including the time to review instructions, search existing data sources, gather and maintain the data needed and complete and review the collection of information. Send comments regarding this burden estimate or any other aspect of this information collection, including suggestions for reducing this burden, to:

Department of Health and Human Services Food and Drug Administration Office of Chief Information Officer Paperwork Reduction Act (PRA) Staff PRAStaff@fda.hhs.gov

"An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a currently valid OMB number."

3

Image /page/3/Picture/0 description: The image shows the logo for Think Surgical. The logo consists of the word "THINK" in a bold, sans-serif font, with a blue vertical line in place of the "I". Below the word "THINK" is the word "SURGICAL" in a smaller, sans-serif font. The logo is simple and modern, and the blue line adds a touch of color.

510(k) SUMMARY

Applicant Information:

Owner Name:THINK Surgical, Inc.
Address:47201 Lakeview Blvd., Fremont, CA 94538
Phone number:510-249-2337
Fax number:510-249-2396
Establishment Registration Number:3000719653
Contact Person:Meliha Mulalic
Date Prepared:13 November 2020

Device Information:

Device Classification:Class II
Trade Name:TSolution® One Total Knee Application
Common name:Orthopedic Stereotaxic Instrument
Classification name:Stereotaxic Instrument
Regulation number:882.4560
Product Code:OLO

Predicate and Reference Devices:

The TSolution® One Total Knee Application is substantially equivalent in intended use, Indications for Use, design, materials, technology, operational principles and performance to the TSolution One® Total Knee Application cleared via K201255 (primary predicate) and supported with K191369 (reference device).

Device Modification:

The TSolution One Total Knee Application includes a series of incremental hardware and software changes from the previously cleared predicate. These changes have been implemented for the following reasons: to enhance system efficiency and consistency, to enhance the flexibility and ease of use of the system, and to improve the cybersecurity and aesthetics of the system.

Device Description:

Like its predicate, the TSolution One® Total Knee Application is a three-dimensional, graphical, preoperative planning workstation and implementation tool for treatment of patients who require total joint arthroplasty. The device is intended as an alternative to manual template planning and preparation of the bone with patients requiring primary total knee arthroplasty (TKA).

4

Image /page/4/Picture/0 description: The image shows the logo for Think Surgical. The logo consists of the word "THINK" in a bold, sans-serif font, with the "I" replaced by a blue, elongated triangle pointing upwards. Below the word "THINK" is the word "SURGICAL" in a smaller, sans-serif font. A registered trademark symbol is located to the right of the letter "K".

The TSolution One® Total Knee Application consists of TPLAN and TCAT. TPLAN is a three-dimensional (3D) preoperative planning workstation that aids a surgeon in planning the position and orientation of the implant components relative to 3D models of the patient's anatomy. TCAT consists of an electromechanical arm, an arm base including control electronics and computer, a display monitor, operating software, pendant control, and tools and accessories, for the implementation of the preoperative plan. TCAT and TPLAN when used according to the instructions for use, make submillimeter precision bone preparation possible before and during TKA surgical procedures.

Intended Use / Indications for Use:

The TSolution One® Total Knee Application is intended for use as a device that uses diagnostic images of the patient acquired specifically to assist the physician with preoperative planning and to provide orientation and reference information during intraoperative procedures. The robotic surgical tool, under the direction of the surgeon, precisely implements the presurgical software plan.

The preoperative planning software and robotic surgical tool are used as an alternative to manual planning and resecting techniques for the distal femur and proximal tibia preparation in primary total knee arthroplasty (TKA).

The TSolution One® Total Knee Application is indicated for orthopedic procedures in which resecting techniques used for the distal femur and proximal tibia may be considered to be as safe and effective and where references to rigid anatomical structures mav be made.

The TSolution One® Total Knee Application is also intended to assist the surgeon in determining reference alignment axes in relation to anatomical and instrumentation structures during stereotactic orthopedic surgical procedures. The TSolution One® Total Knee Application facilitates accurate positioning of TKA implants, relative to these alignment axes.

The TSolution One® Total Knee Application is compatible with the following Knee Implant Systems:

  • Zimmer Persona™ Knee System ●
  • Corin Unity Knee System
  • . Aesculap Columbus Knee System
  • DJO Surgical® EMPOWR 3D Knee® System ●
  • . United U2 Knee System

Substantial Equivalence:

Both the TSolution One® Total Knee Application, the subject of this submission, and the predicate device have the same intended use. Both are intended for use as devices that use diagnostic images of the patient acquired specifically to assist the physician with presurgical planning and to provide orientation and reference information during intraoperative procedures. The robotic surgical tool, under the direction of the surgeon, precisely implements the presurgical software plan. The difference between the new

5

Image /page/5/Picture/0 description: The image shows the logo for Think Surgical. The logo consists of the word "THINK" in a bold, sans-serif font, with a blue triangle replacing the "I". Below the word "THINK" is the word "SURGICAL" in a smaller, sans-serif font. The logo is simple and modern, and the blue triangle adds a touch of color and visual interest.

TSolution One® Total Knee Application Special 510(k) Submission

device and the predicates is that the new device incorporates a series of incremental changes in the hardware and software that enhance system efficiency and consistency, enhance the flexibility and ease of use of the system, and improve the cybersecurity and aesthetics of the system. None of these changes either individually or in the aggregate alter the intended use, indications for use, design, materials, technology or operational principles of the TSolution One Total Knee Application.

The Indications for Use of the new device and its predicate are identical.

The results of the analysis demonstrate that any risks identified have been mitigated to acceptable levels and no new clinical hazards arise as a result of the changes. Additionally, the modifications made to the predicate device do not raise any new questions of safety or effectiveness or increase the overall risk profile of the device.

Performance testing to verify the cutting accuracy of the subject device was conducted following similar test methods and acceptance criteria to those used for the predicate device. Electromagnetic Compatibility and Electrical Safety testing met the requirements of applicable IEC standards. Validation testing, with methods and acceptance criteria similar to that used for the predicate device, was conducted using simulated surgical testing in a cadaver model and all test criteria were met. Biocompatibility Testing performed according to the ISO 10993-1:2009 standard was completed on any new patient contacting materials. All of this testing demonstrated that the TSolution One® Total Knee Application met the test criteria and specifications of the predicate device.

| Product | TSolution One Total
Knee Application | TSolution One Total
Knee Application | Substantial
Equivalence
Conclusion |
|------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------|
| 510(k) number | Subject Device | K201255 | |
| Manufacturer | THINK Surgical Inc. | THINK Surgical Inc. | |
| Technological
Characteristics | | | |
| -Patient Imaging | CT Scan | CT Scan | SAME |
| -User Controls | Keyboard, mouse,
Pendant with
mechanically latched Stop
Button | Keyboard, mouse,
Pendant with
mechanically latched
Stop Button | SAME |
| -Preoperative
planning
workstation | TPLAN three-dimensional
preoperative planning
workstation | TPLAN three-dimensional
preoperative planning
workstation | SAME |
| -Pre-surgical Plan | CT images used to create
a 3D model of the bone,
library of FDA cleared
components used to
develop optimal implant
size and location | CT images used to create
a 3D model of the bone,
library of FDA cleared
components used to
develop optimal implant
size and location | SAME |
| Product | TSolution One Total
Knee Application | TSolution One Total
Knee Application | Substantial
Equivalence
Conclusion |
| | | K201255 | |
| 510(k) number | Subject Device | K201255 | |
| Manufacturer | THINK Surgical Inc. | THINK Surgical Inc. | |
| -Surgical Plan
Data | High level operative plan
based on preoperative
plan with predetermined
control file developed to
control the robotic arm. | High level operative plan
based on preoperative
plan with predetermined
control file developed to
control the robotic arm. | SAME |
| -Surgical
Exposure | Similar to traditional
surgical exposure for the
anatomic site | Similar to traditional
surgical exposure for the
anatomic site | SAME |
| Electromechanical
arm to implement
pre-surgical plan | TCAT electromechanical
arm system implements
pre-surgical plan | TCAT electromechanical
arm system implements
pre-surgical plan | SAME |
| -Patient/Robot
Registration | Pinless point to surface
registration with
mechanical tracking.
Percutaneous probe thin
enough to make contact
via direct puncture
through skin. | Pinless point to surface
registration with
mechanical tracking.
Percutaneous probe thin
enough to make contact
via direct puncture
through skin. | SAME |
| -Bone Motion
Recovery | Two bone motion
recovery markers are
used to recover
registration after bone
motion. | Two bone motion
recovery markers are
used to recover
registration after bone
motion. | SAME |
| -Compatible Knee
Implant Systems | -Zimmer Persona™ Knee
System

-Corin Unity Knee System

-Aesculap
Columbus Knee System

-DJO Surgical® EMPOWR
3D Knee® System

-United U2 Knee System | -Zimmer Persona™ Knee
System

-Corin Unity Knee System

-Aesculap
Columbus Knee System

-DJO Surgical®
EMPOWR 3D Knee®
System

-United U2 Knee System | SAME |
| Performance
Testing | | | |
| -Cutting Accuracy
Verification | Passed | Passed | SAME |
| -Cadaver Lab
Validation Testing | Passed | Passed | SAME |
| -Software Testing | Passed | Passed | SAME |
| -Electromagnetic
Compatibility and
Electrical Safety | Passed | Passed | SAME |
| Product | TSolution One Total Knee Application | TSolution One Total Knee Application | Substantial
Equivalence
Conclusion |
| 510(k) number | Subject Device | K201255 | |
| Manufacturer | THINK Surgical Inc. | THINK Surgical Inc. | |
| _Biocompatibility
Testing on
Changed
Materials | Passed | N/A | SAME |

Substantial equivalence in technological characteristic and performance of the TSolution One® Total Knee Application to the predicate device is outlined in the table below:

6

Image /page/6/Picture/0 description: The image shows the logo for Think Surgical. The logo is composed of the word "THINK" in a bold, sans-serif font, with a blue triangle replacing the "I". Below the word "THINK" is the word "SURGICAL" in a smaller, sans-serif font. The logo is simple and modern, and the blue triangle adds a touch of color and visual interest.

7

Image /page/7/Picture/0 description: The image shows the logo for Think Surgical. The logo consists of the word "THINK" in bold, sans-serif font, with the "I" replaced by a blue, downward-pointing triangle. Below the word "THINK" is the word "SURGICAL" in a smaller, sans-serif font.

TSolution One® Total Knee Application Special 510(k) Submission

Conclusion

The TSolution One® Total Knee Application is substantially equivalent to the predicate, TSolution One® Total Knee Application (K201255), in the following ways: it has the same intended use, the same technological characteristics and operating principles, incorporates the same design and materials. Performance testing and risk analysis has demonstrated that the acceptance criteria of the TSolution One® Total Knee Application are equivalent to the predicate device. The TSolution One® Total Knee Application is as safe and effective as the predicate device and does not raise any new questions of safety and effectiveness; therefore, a determination of Substantial Equivalence is supported.