# EDGAR Filing Document

**Accession Number:** 0001326190
**File Stem:** 0001104659-26-047053
**Filing Date:** 2026-4
**Character Count:** 20962
**Document Hash:** be5e37ed0c6818890830866a3f060616
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-26-047053.hdr.sgml**: 20260422

**ACCESSION NUMBER**: 0001104659-26-047053

**CONFORMED SUBMISSION TYPE**: S-3MEF

**PUBLIC DOCUMENT COUNT**: 14

**FILED AS OF DATE**: 20260422

**DATE AS OF CHANGE**: 20260422

**EFFECTIVENESS DATE**: 20260422

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Altimmune, Inc.
- **CENTRAL INDEX KEY:** 0001326190
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 202726770
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-3MEF
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-295254
- **FILM NUMBER:** 26885281

**BUSINESS ADDRESS:**
- **STREET 1:** 910 CLOPPER ROAD
- **STREET 2:** SUITE 201S
- **CITY:** GAITHERSBURG
- **STATE:** MD
- **ZIP:** 20878
- **BUSINESS PHONE:** 2406541450

**MAIL ADDRESS:**
- **STREET 1:** 910 CLOPPER ROAD
- **STREET 2:** SUITE 201S
- **CITY:** GAITHERSBURG
- **STATE:** MD
- **ZIP:** 20878

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PHARMATHENE, INC
- **DATE OF NAME CHANGE:** 20071016

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** HEALTHCARE ACQUISITION CORP
- **DATE OF NAME CHANGE:** 20050505

**As filed with the Securities and Exchange Commission on April 22, 2026.** 

**Registration No. 333-** 

**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**Washington, D.C. 20549** 

**FORM S-3**

**REGISTRATION STATEMENT** 

***UNDER***

***THE SECURITIES ACT OF 1933***

**Altimmune, Inc.** 

**(Exact name of registrant as specified in its charter)** 

---

| | |
|:---|:---|
| **Delaware** | **20-2726770** |
| **(State or other jurisdiction of**<br> **incorporation or organization)** | **(I.R.S. Employer**<br> **Identification Number)** |

---

**910 Clopper Road, Suite 201S**

**Gaithersburg, Maryland 20878**

**(240) 654-1450**

**(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)** 

**Jerome Durso**

**President and Chief Executive Officer** 

**Altimmune, Inc. 910 Clopper Road, Suite 201S**

**Gaithersburg, Maryland 20878**

**(240) 654-1450 (Name, address, including zip code, and telephone number, including area code, of agent for service)** 

***With copies to:***

**Joseph C. Theis, Jr.** 

**Justin S. Anslow** 

**Goodwin Procter LLP** 

**100 Northern Avenue** 

**Boston, Massachusetts 02210** 

**Telephone: (617) 570-1000**

**Approximate date of commencement of proposed sale to the public:** From time to time after this registration statement becomes effective.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ◻

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box:⌧

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.⌧ 333-291329

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.◻

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.◻

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.◻

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ¨ | Accelerated filer | ¨ |
| Non-accelerated filer | x | Smaller reporting company | x |
|  |  | Emerging growth company | ¨ |

---

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.◻

**The Registration Statement shall become effective upon filing in accordance with Rule 462(b) under the Securities Act of 1933, as amended.** 

**EXPLANATORY NOTE AND INCORPORATION OF** 

**CERTAIN INFORMATION BY REFERENCE** 

Pursuant to Rule 462(b) under the Securities Act of 1933, as amended, Altimmune, Inc. (the "Registrant") is filing this Registration Statement on Form S-3 (this "Registration Statement") with the Securities and Exchange Commission (the "Commission"). This Registration Statement relates to the public offering of securities contemplated by the Registration Statement on Form S-3 (File No. 333-291329) (the "Prior Registration Statement"), which the Registrant initially filed with the Commission on November 6, 2025, and which the Commission declared effective on December 5, 2025.

The Registrant is filing this Registration Statement for the sole purpose of increasing the aggregate amount of securities offered by the Registrant by a proposed aggregate offering price of $65,000,000. The additional securities that are being registered for issuance and sale are in an amount and at a price that together represent no more than 20% of the maximum aggregate offering price of unsold securities under the Prior Registration Statement. The information set forth in the Prior Registration Statement and all exhibits to the Prior Registration Statement are hereby incorporated by reference into this Registration Statement.

The required opinion and consents are listed on the Exhibit Index below and filed herewith or incorporated by reference herein.

**PART II** 

**INFORMATION NOT REQUIRED IN PROSPECTUS** 

**Item 16.** **Exhibits** 

All exhibits filed with or incorporated by reference in the Registration Statement on Form S-3 (File No. 333-291329) are incorporated by reference into, and shall be deemed a part of, this Registration Statement, and the following additional exhibits are filed herewith, as part of this Registration Statement:

---

| | |
|:---|:---|
| **Exhibit<br> No.** | **Description** |
| [5.1](tm2612458d1_ex5-1.htm) | [Opinion of Goodwin Procter LLP.](tm2612458d1_ex5-1.htm) |
| [23.1](tm2612458d1_ex23-1.htm) | [Consent of Ernst & Young LLP Independent Registered Public Accounting Firm.](tm2612458d1_ex23-1.htm) |
| [23.2](https://www.sec.gov/Archives/edgar/data/1690585/000119312526027273/d53438dex51.htm) | [Consent of Goodwin Procter LLP (see Exhibit 5.1).](https://www.sec.gov/Archives/edgar/data/1690585/000119312526027273/d53438dex51.htm) |
| [24.1](https://www.sec.gov/Archives/edgar/data/1690585/000119312526027273/d53438ds3.htm#sig) | [Power of Attorney (incorporated by reference to Exhibit 24.1 to the Prior Registration Statement).](https://www.sec.gov/Archives/edgar/data/1690585/000119312526027273/d53438ds3.htm#sig) |
| [107](tm2612458d1_ex-filingfees.htm) | [Filing Fee Table.](tm2612458d1_ex-filingfees.htm) |

---

**SIGNATURES** 

Pursuant to the requirements of the Securities Act of 1933, the registrant has duly caused this Registration Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto duly authorized, in Gaithersburg, Maryland, on the 22<sup>nd</sup> day of April, 2026.

---

| | |
|:---|:---|
| **Altimmune, Inc.** | **Altimmune, Inc.** |
| By: | /s/ Jerome Durso  |
|  | Jerome Durso |
|  | President and Chief Executive Officer |

---

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities and on the dates indicated.

---

| | | |
|:---|:---|:---|
| **Signatures** | **Title** | **Date** |
| /s/ Jerome Durso | President, Chief Executive Officer and Chairman of the Board |  |
| Jerome Durso | (*Principal Executive Officer*) | April 22, 2026 |
| /s/ Gregory Weaver | Chief Financial Officer |  |
| Gregory Weaver | *(Principal Financial Officer and Principal Accounting Officer)* | April 22, 2026 |
| \* |  |  |
| John Gill | Director | April 22, 2026 |
| \* |  |  |
| Philip Hodges | Director | April 22, 2026 |
| \* |  |  |
| Diane Jorkasky, M.D. | Director | April 22, 2026 |
| \* |  |  |
| Teri Lawver | Director | April 22, 2026 |
| \* |  |  |
| Wayne Pisano | Director | April 22, 2026 |
| \* |  |  |
| Mitchel Sayare, Ph.D. | Director | April 22, 2026 |
| \* |  |  |
| Klaus O. Schafer, MD. | Director | April 22, 2026 |
| \* |  |  |
| Catherine Sohn, Pharm D | Director | April 22, 2026 |

---

---

| | |
|:---|:---|
| \*By: | /s/ Gregory Weaver |
|  | Gregory Weaver |
|  | *Attorney-in-fact* |

---

## Exhibit 5.1

**Exhibit 5.1**

---

| | |
|:---|:---|
| ![](tm2612458d1_ex5-1img001.jpg) | Goodwin Procter LLP |
| ![](tm2612458d1_ex5-1img001.jpg) | 100 Northern Avenue<br> Boston, MA 02210 |
| ![](tm2612458d1_ex5-1img001.jpg) |  |
| ![](tm2612458d1_ex5-1img001.jpg) | goodwinlaw.com |
| ![](tm2612458d1_ex5-1img001.jpg) | +1 617 570 1000 |

---

April 22, 2026

Altimmune, Inc.

910 Clopper Road, Suite 201S

Gaithersburg, MD 20878

Re: <u>Securities Being Registered under Registration Statement on Form S-3</u>

We have acted as counsel to you in connection with your filing of (i) a Registration Statement on Form S-3 (File No. 333-291329) (as amended or supplemented, the "Initial Registration Statement") pursuant to the Securities Act of 1933, as amended (the "Securities Act"), and (ii) a Registration Statement on Form S-3 filed pursuant to Rule 462(b) promulgated under the Securities Act relating to the Initial Registration Statement (the "462(b) Registration Statement" and, together with the Initial Registration Statement, the "Registration Statement"), relating to the offering by Altimmune, Inc., a Delaware corporation (the "Company"), of up to $65,000,000 of any combination of (i) the Company's common stock, par value $0.0001 per share (the "Common Stock"), (ii) warrants to purchase Common Stock or Units (as defined below) ("Warrants"), and (iii) units, comprised of Common Stock, Warrants and other securities in any combination ("Units"). The Common Stock, Warrants and Units are sometimes referred to collectively herein as the "Securities.".

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinions set forth below, on certificates of officers of the Company.

The opinions set forth below are limited to the Delaware General Corporation Law and the law of New York.

For purposes of the opinions set forth below, without limiting any other exceptions or qualifications set forth herein, we have assumed that (i) each of the Warrants and Units, and the warrant agreements, unit agreements and other agreements governing Securities offered pursuant to the Registration Statement will be governed by the internal law of New York and (ii) after the issuance of any Securities offered pursuant to the Registration Statement, the total number of issued shares of Common Stock, together with the total number of shares of such stock issuable upon the exercise, exchange, conversion or settlement, as the case may be, of any exercisable, exchangeable or convertible security (including without limitation any Unit), as the case may be, then outstanding, will not exceed the total number of authorized shares of Common Stock then available for issuance under the Company's certificate of incorporation as then in effect (the "Charter").

Altimmune, Inc.

April 22, 2026

For purposes of the opinions set forth below, we refer to the following as the "Future Approval and Issuance" of Securities:

&nbsp;&nbsp;&nbsp;&nbsp;· with respect to any of the Securities, (a) the approval by the Company of the amount, terms and issuance of such Securities (the "Approval")
and (b) the issuance of such Securities in accordance with the Approval upon the receipt by the Company of the consideration (which, in
the case of shares of Common Stock, is not less than the par value of such shares) to be paid in accordance with the Approval; and

&nbsp;&nbsp;&nbsp;&nbsp;· with respect to Warrants or Units, (a) the approval, execution and delivery by the Company and any other parties thereto of any agreement
under which such Securities are to be issued, and (b) the establishment of the terms of such Securities and the issuance of such Securities
in conformity with those terms, the terms of any applicable agreement and applicable law.

Based upon the foregoing, and subject to the additional qualifications set forth below, we are of the opinion that:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1. Upon the Future Approval and Issuance of shares of Common Stock, such shares of Common Stock will be validly issued, fully paid and
nonassessable.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2. Upon the Future Approval and Issuance of Warrants, such Warrants will be valid and binding obligations of the Company.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3. Upon the Future Approval and Issuance of Units, such Units will be valid and binding obligations of the Company.

The opinions expressed above are subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other similar laws of general application affecting the rights and remedies of creditors and to general principles of equity.

This opinion letter and the opinions it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 Business Lawyer 815 (Summer 2019).

Altimmune, Inc.

April 22, 2026

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the 462(b) Registration Statement and to the references to our firm under the caption "Legal Matters" in the Initial Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

---

| |
|:---|
| Very truly yours, |
| /s/ Goodwin Procter LLP |
| GOODWIN PROCTER LLP |

---

## Exhibit 23.1

**Exhibit 23.1**

**Consent of Independent Registered Public Accounting Firm**

We consent to the incorporation by reference in the Registration Statement on Form S-3 filed pursuant to Rule 462(b) of the Securities Act of 1933 of the reference to our firm under the caption "Experts" and to the incorporation by reference of our report dated March 6, 2026, with respect to the consolidated financial statements of Altimmune Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2025, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Iselin, New Jersey

April 22, 2026

## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

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| |
|:---|
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Calculation of Filing Fee Tables**  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **S-3**  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Altimmune, Inc.**  |

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| | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|
| | | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Security Type**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Security Class Title**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Fee Calculation or Carry Forward Rule**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Maximum Aggregate Offering Price**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Fee Rate**  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Amount of Registration Fee**  |
| **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** | **Newly Registered Securities** |
|  |  | Equity | Common Stock, par value $0.0001 per share | 457(o) |  |  |  |
|  |  | Other | Warrants | 457(o) |  |  |  |
|  |  | Other | Units | 457(o) |  |  |  |
| Fees to be Paid | 1 | Unallocated (Universal) Shelf |  | 457(o) | $65000000.00 | 0.0001381 | $8976.50 |
| Fees Previously Paid |  |  |  |  |  |  |  |
| **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** | **Carry Forward Securities** |
| Carry Forward Securities |  |  |  |  |  |  |  |
|  |  |  | Total Offering Amounts: | Total Offering Amounts: | $65000000.00  |  | $8976.50  |
|  |  |  | Total Fees Previously Paid:  | Total Fees Previously Paid:  |  |  | $0.00  |
|  |  |  | Total Fee Offsets:  | Total Fee Offsets:  |  |  | $0.00  |
|  |  |  | Net Fee Due:  | Net Fee Due:  |  |  | $8976.50  |

---

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **Offering Note** <br>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <sup>1</sup> The Registrant previously registered the offer and sale of certain securities, including its common stock, par value $0.0001 per share, having a proposed maximum aggregate offering price of $400,000,000 pursuant to Registration Statement on Form S-3 (File No. 333-291329), which the Registrant initially filed with the Commission on November 6, 2026, and which the Commission declared effective on December 5, 2026 (the "Prior Registration Statement"). As of the date hereof, a balance of $325,000,000 of such securities remains unsold under the Prior Registration Statement. In accordance with Rule 462(b) under the Securities Act of 1933, as amended, and General Instruction IV(A) of Form S-3, the Registrant is hereby registering the offer and sale of an additional $65,000,000 of its shares of common stock and warrants to purchase common stock to be offered as a unit. The additional securities that are being registered for issuance and sale are in an amount and at a price that together represent no more than 20% of the maximum aggregate offering price of unsold securities under the Prior Registration Statement.

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| |
|:---|
| |
| **Rules 457(b) and 0-11(a)(2)** |
| Fee Offset Claims |
| Fee Offset Sources |
| **Rule 457(p)** |
| Fee Offset Claims |
| Fee Offset Sources |

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