Vericert Manual

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Vericert Manual

Table of Contents

1 Introduction

Vericert translates C code into a hardware description language called Verilog, which can then be synthesised into hardware, to be placed onto a field-programmable gate array (FPGA) or application-specific integrated circuit (ASIC).


Figure 1.1: Current design of Vericert, where HTL is an intermediate language representing a finite state machine with data-path (FSMD) and Verilog is the target language.

The design shown in Figure Figure 1.1 shows how Vericert leverages an existing verified C compiler called CompCert to perform this translation.

Copyright (C) 2019-2022 Yann Herklotz.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

2 Building Vericert

To build Vericert, the provided Makefile can be used. External dependencies are needed to build the project, which can be pulled in automatically with nix using the provided default.nix and shell.nix files.

The project is written in Coq, a theorem prover, which is extracted to OCaml so that it can then be compiled and executed. The dependencies of this project are the following:

These dependencies can be installed manually, or automatically through Nix.

2.1 Downloading Vericert and CompCert

CompCert is added as a submodule in the ‘lib/CompCert’ directory. It is needed to run the build process below, as it is the one dependency that is not downloaded by nix, and has to be downloaded together with the repository. To clone CompCert together with this project, and check it out at the correct revision, you can run:

git clone -b v1.2.2 --recursive

If the repository is already cloned, you can run the following command to make sure that CompCert is also downloaded and the correct branch is checked out:

git checkout v1.2.2
git submodule update --init

2.2 Setting up Nix

Nix is a package manager that can create an isolated environment so that the builds are reproducible. Once nix is installed, it can be used in the following way.

To open a shell which includes all the necessary dependencies, one can use:


which will open a shell that has all the dependencies loaded.

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2.3 Makefile build

If the dependencies were installed manually, or if one is in the ‘nix-shell’, the project can be built by running:

make -j8

and installed locally, or under the ‘PREFIX’ location using:

make install

Which will install the binary in ‘./bin/vericert’ by default. However, this can be changed by changing the ‘PREFIX’ environment variable, in which case the binary will be installed in ‘$PREFIX/bin/vericert’.

2.4 Testing

To test out vericert you can try the following examples which are in the test folder using the following:

./bin/vericert test/loop.c -o loop.v
./bin/vericert test/conditional.c -o conditional.v
./bin/vericert test/add.c -o add.v

Or by running the test suite using the following command:

make test

3 Using Vericert

Vericert can be used to translate a subset of C into Verilog. As a simple example, consider the following C file (main.c):

void matrix_multiply(int first[2][2], int second[2][2], int multiply[2][2]) {
    int sum = 0;
    for (int c = 0; c < 2; c++) {
        for (int d = 0; d < 2; d++) {
            for (int k = 0; k < 2; k++) {
                sum = sum + first[c][k]*second[k][d];
            multiply[c][d] = sum;
            sum = 0;

int main() {
    int f[2][2] = {{1, 2}, {3, 4}};
    int s[2][2] = {{5, 6}, {7, 8}};
    int m[2][2] = {{0, 0}, {0, 0}};

    matrix_multiply(f, s, m);
    return m[1][1];

It can be compiled using the following command, assuming that vericert is somewhere on the path.

vericert main.c -o main.v

The Verilog file contains a top-level test-bench, which can be given to any Verilog simulator to simulate the hardware, which should give the same result as executing the C code. Using Icarus Verilog as an example:

iverilog -o main_v main.v

When executing, it should therefore print the following:

$ ./main_v
finished: 50

This gives the same result as executing the C in the following way:

$ gcc -o main_c main.c
$ ./main_c
$ echo $?

3.1 Man pages

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3.1.1 NAME

vericert - A formally verified high-level synthesis tool.

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vericert [ OPTION ]… [ FILE ]…

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  1. HLS Options:

    Do not use HLS and generate standard flow


    Simulate the result with the Verilog semantics


    Add debug logic to the Verilog


    initialise the stack to all 0s

  2. HLS Optimisations:

    Schedule the resulting hardware [off]


    If-conversion optimisation [off]

  3. General options:
    -stdlib <dir>

    Set the path of the Compcert run-time library


    Print external commands before invoking them


    Show the time spent in various compiler passes


    Print the version string and exit

    -target <value>

    Generate code for the given target

    -conf <file>

    Read configuration from file


    Read command line options from <file>

  4. Tracing Options:

    Save C file after preprocessing in <file>.i


    Save C file after parsing and elaboration in <file>.parsed.c


    Save generated C in <file>.compcert.c


    Save generated Clight in <file>.light.c


    Save generated Cminor in <file>.cm


    Save RTL at various optimization points in <file>.rtl.<n>


    Save RTLBlock <file>.rtlblock


    Save HTL before Verilog generation <file>.htl


    Save LTL after register allocation in <file>.ltl


    Save generated Mach code in <file>.mach


    Save generated assembly in <file>.s


    Save all generated intermediate files in <file>.<ext>


    Save info for post-linking validation in <file>.json

    -o <file>

    Generate output in <file>

  5. Diagnostic options:

    Enable all warnings


    Enable the specific <warning>


    Disable the specific <warning>


    Make all warnings into errors


    Turn <warning> into an error


    Turn <warning> into a warning even if -Werror is specified


    Turn all errors into fatal errors aborting the compilation


    Turn on colored diagnostics


    Turn of colored diagnostics


    Maximum number of errors to report


    Print the option name with mappable diagnostics


    Turn of printing of options with mappable diagnostics

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3.1.4 AUTHOR

Written by Yann Herklotz, Michalis Pardalos, James Pollard, Nadesh Ramanathan and John Wickerson.

4 Unreleased Features

The following are unreleased features in Vericert that are currently being worked on and have not been completely proven correct yet. Currently this includes features such as:

This page gives some preliminary information on how the features are implemented and how the proofs for the features are being done. Once these features are properly implemented, they will be added to the proper documentation.

4.1 Scheduling

Scheduling is an optimisation which is used to run various instructions in parallel that are independent to each other.

4.2 Operation Chaining

Operation chaining is an optimisation that can be added on to scheduling and allows for the sequential execution of instructions in a clock cycle, while executing other instructions in parallel in the same clock cycle.

4.3 If-conversion

If-conversion is an optimisation which can turn code with simple control flow into a single block (called a hyper-block), using predicated instructions.

4.4 Functions

Functions are currently only inlined in Vericert, however, we are working on a proper interface to integrate function calls into the hardware.

5 Coq Style Guide

This style guide was taken from Silveroak, it outlines code style for Coq code in this repository. There are certainly other valid strategies and opinions on Coq code style; this is laid out purely in the name of consistency. For a visual example of the style, see the example at the bottom of this file.

5.1 Code organization

5.1.2 Import statements

  • Require Import’ statements should all go at the top of the file, followed by file-wide ‘Import’ statements.
    • =Import=s often contain notations or typeclass instances that might override notations or instances from another library, so it’s nice to highlight them separately.
  • One ‘Require Import’ statement per line; it’s easier to scan that way.
  • Require Import’ statements should use "fully-qualified" names (e.g. ‘Require Import Coq.ZArith.ZArith’ instead of ‘Require Import ZArith’).
    • Use the ‘Locate’ command to find the fully-qualified name!
  • Require Import’’s should go in the following order:
    1. Standard library dependencies (start with ‘Coq.’)
    2. External dependencies (anything outside the current project)
    3. Same-project dependencies
  • Require Import’’s with the same root library (the name before the first ‘.’) should be grouped together. Within each root-library group, they should be in alphabetical order (so ‘Coq.Lists.List’ before ‘Coq.ZArith.ZArith’).

5.1.3 Notations and scopes

  • Any file-wide ‘Local Open Scope’’s should come immediately after the =Import=s (see example).
    • Always use ‘Local Open Scope’; just ‘Open Scope’ will sneakily open the scope for those who import your file.
  • Put notations in their own separate modules or files, so that those who import your file can choose whether or not they want the notations.
    • Conflicting notations can cause a lot of headache, so it comes in very handy to leave this flexibility!

5.2 Formatting

5.2.1 Line length

  • Maximum line length 80 characters.
    • Many Coq IDE setups divide the screen in half vertically and use only half to display source code, so more than 80 characters can be genuinely hard to read on a laptop.

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5.2.2 Whitespace and indentation

  • No trailing whitespace.
  • Spaces, not tabs.
  • Files should end with a newline.
    • Many editors do this automatically on save.
  • Colons may be either "English-spaced", with no space before the colon and one space after (‘x: nat’) or "French-spaced", with one space before and after (‘x : nat’).
  • Default indentation is 2 spaces.
    • Keeping this small prevents complex proofs from being indented ridiculously far, and matches IDE defaults.
  • Use 2-space indents if inserting a line break immediately after:
    • Proof.
    • fun <...> =>
    • forall <...>,
    • exists <....>,
  • The style for indenting arguments in function application depends on where you make a line break. If you make the line break immediately after the function name, use a 2-space indent. However, if you make it after one or more arguments, align the next line with the first argument:
       1 2)
    (Z.pow 1 2 3
           4 5 6)
  • Inductive’ cases should not be indented. Example:
    Inductive Foo : Type :=
    | FooA : Foo
    | FooB : Foo
  • match’ or ‘lazymatch’ cases should line up with the "m" in ‘match’ or "l" in ‘lazymatch’, as in the following examples:
    match x with
    | 3 => true
    | _ => false
    lazymatch x with
    | 3 => idtac
    | _ => fail "Not equal to 3:" x
    repeat match goal with
           | _ => progress subst
           | _ => reflexivity
    do 2 lazymatch goal with
         | |- context [eq] => idtac

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5.3 Definitions and Fixpoints

  • It’s okay to leave the return type of ‘Definition’’s and ‘Fixpoint’’s implicit (e.g. Definition x := 5 instead of Definition x : nat := 5) when the type is very simple or obvious (for instance, the definition is in a file which deals exclusively with operations on ‘Z’).

5.4 Inductives

  • The ‘.’ ending an ‘Inductive’ can be either on the same line as the last case or on its own line immediately below. That is, both of the following are acceptable:
    Inductive Foo : Type :=
    | FooA : Foo
    | FooB : Foo
    Inductive Foo : Type :=
    | FooA : Foo
    | FooB : Foo.

5.5 Lemma/Theorem statements

  • Generally, use ‘Theorem’ for the most important, top-level facts you prove and ‘Lemma’ for everything else.
  • Insert a line break after the colon in the lemma statement.
  • Insert a line break after the comma for ‘forall’ or ‘exist’ quantifiers.
  • Implication arrows (‘->’) should share a line with the previous hypothesis, not the following one.
  • There is no need to make a line break after every ‘->’; short preconditions may share a line.

5.6 Proofs and tactics

  • Use the ‘Proof’ command (lined up vertically with ‘Lemma’ or ‘Theorem’ it corresponds to) to open a proof, and indent the first line after it 2 spaces.
  • Very small proofs (where ‘Proof. <tactics> Qed.’ is <= 80 characters) can go all in one line.
  • When ending a proof, align the ending statement (‘Qed’, ‘Admitted’, etc.) with ‘Proof’.
  • Avoid referring to autogenerated names (e.g. ‘H0’, ‘n0’). It’s okay to let Coq generate these names, but you should not explicitly refer to them in your proof. So ‘intros; my_solver’ is fine, but ‘intros; apply H1; my_solver’ is not fine.
    • You can force a non-autogenerated name by either putting the variable before the colon in the lemma statement (‘Lemma foo x : ...’ instead of ‘Lemma foo : forall x, ...’), or by passing arguments to ‘intros’ (e.g. ‘intros ? x’ to name the second argument ‘x’)
  • This way, the proof won’t break when new hypotheses are added or autogenerated variable names change.
  • Use curly braces ‘{}’ for subgoals, instead of bullets.
  • Never write tactics with more than one subgoal focused. This can make the proof very confusing to step through! If you have more than one subgoal, use curly braces.
  • Consider adding a comment after the opening curly brace that explains what case you’re in (see example).
    • This is not necessary for small subgoals but can help show the major lines of reasoning in large proofs.
  • If invoking a tactic that is expected to return multiple subgoals, use ‘[ | ... | ]’ before the ‘.’ to explicitly specify how many subgoals you expect.
    • Examples: ‘split; [ | ].’ ‘induction z; [ | | ].
    • This helps make code more maintainable, because it fails immediately if your tactic no longer solves as many subgoals as expected (or unexpectedly solves more).
  • If invoking a string of tactics (composed by ‘;’) that will break the goal into multiple subgoals and then solve all but one, still use ‘[ ]’ to enforce that all but one goal is solved.
    • Example: ‘split; try lia; [ ]’.
  • Tactics that consist only of ‘repeat’-ing a procedure (e.g. ‘repeat match’, ‘repeat first’) should factor out a single step of that procedure a separate tactic called ‘<tactic name>_step’, because the single-step version is much easier to debug. For instance:
    Ltac crush_step :=
      match goal with
      | _ => progress subst
      | _ => reflexivity
    Ltac crush := repeat crush_step.

5.7 Naming

  • Helper proofs about standard library datatypes should go in a module that is named to match the standard library module (see example).
    • This makes the helper proofs look like standard-library ones, which is helpful for categorizing them if they’re genuinely at the standard-library level of abstraction.
  • Names of modules should start with capital letters.
  • Names of inductives and their constructors should start with capital letters.
  • Names of other definitions/lemmas should be snake case.

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5.8 Example

A small standalone Coq file that exhibits many of the style points.

 * Vericert: Verified high-level synthesis.
 * Copyright (C) 2021 Name <[email protected]>
 * <License...>

  Require Import Coq.Lists.List.
  Require Import Coq.micromega.Lia.
  Require Import Coq.ZArith.ZArith.
  Import ListNotations.
  Local Open Scope Z_scope.

  (* Helper proofs about standard library integers (Z) go within [Module Z] so
     that they match standard-library Z lemmas when used. *)
  Module Z.
    Lemma pow_3_r x : x ^ 3 = x * x * x.
    Proof. lia. Qed. (* very short proofs can go all on one line *)

    Lemma pow_4_r x : x ^ 4 = x * x * x * x.
      change 4 with (Z.succ (Z.succ (Z.succ (Z.succ 0)))).
      repeat match goal with
             | _ => rewrite Z.pow_1_r
             | _ => rewrite Z.pow_succ_r by lia
             | |- context [x * (?a * ?b)] =>
               replace (x * (a * b)) with (a * b * x) by lia
             | _ => reflexivity
  End Z.
  (* Now we can access the lemmas above as Z.pow_3_r and Z.pow_4_r, as if they
     were in the ZArith library! *)

  Definition bar (x y : Z) := x ^ (y + 1).

  (* example with a painfully manual proof to show case formatting *)
  Lemma bar_upper_bound :
    forall x y a,
      0 <= x <= a -> 0 <= y ->
      0 <= bar x y <= a ^ (y + 1).
    (* avoid referencing autogenerated names by explicitly naming variables *)
    intros x y a Hx Hy. revert y Hy x a Hx.
    (* explicitly indicate # subgoals with [ | ... | ] if > 1 *)
    cbv [bar]; refine (natlike_ind _ _ _); [ | ].
    { (* y = 0 *)
      intros; lia. }
    { (* y = Z.succ _ *)
      rewrite Z.add_succ_l, Z.pow_succ_r by lia.
      { (* 0 <= bar x y *)
        apply Z.mul_nonneg_nonneg; [ lia | ].
        apply Z.pow_nonneg; lia. }
      { (* bar x y < a ^ y *)
        rewrite Z.pow_succ_r by lia.
        apply Z.mul_le_mono_nonneg; try lia;
          [ apply Z.pow_nonneg; lia | ].
        (* For more flexible proofs, use match statements to find hypotheses
           rather than referring to them by autogenerated names like H0. In this
           case, we'll take any hypothesis that applies to and then solves the
           goal. *)
        match goal with H : _ |- _ => apply H; solve [auto] end. } }

  (* Put notations in a separate module or file so that importers can
     decide whether or not to use them. *)
  Module BarNotations.
    Infix "#" := bar (at level 40) : Z_scope.
    Notation "x '##'" := (bar x x) (at level 40) : Z_scope.
  End BarNotations.

Appendix A Index - Features

Jump to:   S  
Index Entry  Section

scheduling: Scheduling

Jump to:   S  

Appendix B GNU Free Documentation License

Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.


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    You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.


    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements."


    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.


    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.


    "Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site.

    "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    "Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

B.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

Copyright (C)  YEAR  YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts.  A copy of the license is included in the section entitled ``GNU
Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with…Texts." line with this:

with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.