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+# Using SWI-Prolog commercially
+
+As of July 2020, SWI-Prolog is managed by SWI-Prolog Solutions b.v.
+as a commercial project.  The mission of SWI-Prolog Solutions b.v.  is
+to help organizations using SWI-Prolog for profit.
+
+
+## Why should I consider SWI-Prolog?
+
+SWI-Prolog, a powerful declarative language, offers a high level of
+abstraction similar to SQL. This abstraction allows for concise code
+that can be developed quickly and maintained easily. Even domain
+experts with minimal training can understand and read the code,
+breaking down the traditional barrier between coders and domain
+experts. As a result, development and maintenance productivity
+significantly increase, allowing you to keep up with evolving business
+needs effortlessly.
+
+Unlike SQL, SWI-Prolog is a versatile language that extends beyond
+accessing relational data. It excels in formal domains, enabling
+reasoning about formal specifications, programming languages,
+business rules, etc. Additionally, it shines in semi-formal domains like
+legal reasoning, reasoning about medical guidelines or robotics.
+
+SWI-Prolog boasts a solid and secure industry-proven core engine. It
+implements most known extensions to the ISO standard core of
+Prolog. The preemptive multi-threading feature efficiently utilizes
+all available cores, ensuring optimal performance.
+
+## Q&A
+
+### Q: What about all reasons not to use Prolog? ...
+
+#### Q: I understand Prolog is dead.  Is that true?
+
+True, various implementations are barely alive.  SWI-Prolog however is
+downloaded about 250,000 times from the [main
+site](https://www.swi-prolog.org/Download.html) each year.  In
+addition it is a package for several Linux distributions, it appears
+on several Windows program download sites and it is a [standard Docker
+library](https://hub.docker.com/_/swipl/), claiming 1M+ downloads.
+We have an active user [forum](https://swi-prolog.discourse.group/)
+with about 1,000 users.  The time to first response on a post rarely
+exceeds an hour.  [OpenHub](https://openhub.net/p/swi-prolog) claims
+nearly 1,500 commits by 25 contributers per year.
+
+#### Q: Prolog is considered hard to learn.  Is that true?
+
+Yes and no.  True, people with only an _imperative_ and _object
+oriented_ background (C++, Java, Python, etc.), Prolog looks alien at first
+sight.  People with a functional programming background are in a much
+better position because pure functional languages like Lisp and
+Haskell share _recursion_ as the main control structure with Prolog.
+People with a mathematical background understand Prolog easily as it
+connects directly to _inductive proof_.  In our experience people with
+no programming background at all deal surprisingly well with Prolog.
+Consider the (toy) example below.  A Python programmer barely
+recognises this as a program, while a logician but also someone
+without programming experience immediately recognises this as a
+correct formalization of the concepts _sister_ and _sibling_.
+
+```
+sister(Sister, Sibling) :-
+	sibling(Sister, Sibling),
+	female(Sister).
+
+sibling(Person1, Person2) :-
+    parent(Person1, Parent),
+	parent(Person2, Parent).
+```
+
+For programmers in the first category, count some weeks before they
+connect the dots.
+
+#### Q: Prolog does not scale.  Is that true?
+
+Briefly, Prolog scales well for what it is designed for and can
+seamlessly use other technology for things it is not designed for.
+Below are some details.
+
+Prolog is not good at some tasks.  Notably tasks that involve
+operations on large arrays (vectors) of uniform numbers such as
+images.   That actually also applies to e.g., Python and is which
+why most of the Python machine learning libraries are coded in C
+or C++, with or without the help of the GPU (using CUDA).
+
+Next, there are tasks for which the naive declarative specification
+does not scale due to a combinatorial explosion.  Such cases are easy
+to predict because the execution model of Prolog (called SLD
+resolution) is easy to understand.  There are generally three ways
+out: _Constraint Logic Programming_, _Tabled (SLG) resolution_ or
+reformulate the specification such that it implements a more efficient
+algorithm.  For example, we can specify _sorting_ as (1) _generate a
+permutation_ and (2) _check the list is ordered_.  We can also specify
+it as (1) _split the list in two_, (2) _sort the two smaller lists_
+and (3) _merge the two ordered lists_.  This recursive specification
+stops by stating that the sorted version of a list with no or one
+element is the list itself.  Both work, but where the complexity of
+the first is O(n!), the complexity of the second is O(log(n)).  In
+other words, while the specification _describes_ the logical relation
+declaratively, the transparent and predictable resolution causes the
+same description to _implicitly encode an algorithm_.
+
+SWI-Prolog does scales to tens of millions of facts and automatically
+builds _indexes_ to access large datasets efficiently.  The indexes
+are build _just in time_ based on the actual runtime behavior of your
+code.  If that is not enough, you can connect it seamlessly to
+external data sources such as relational databases, graph stores, etc.
+For example, an SQL query can easily be wrapped as a predicate, after
+which it behaves exactly the same as a normal Prolog predicate.
+Prolog does not suffer from the Object–relational _impedance mismatch_
+because Prolog itself is _relational_.  Similarly, large arrays may be
+handled through the C, C++, C#, Java, Rust or Python interface, after
+which the result (again) fits naturally in Prolog's eco system.
+
+#### Q: Where do I find Prolog programmers?
+
+It is unfortunately true than experienced Prolog programmers are not
+readily available everywhere.  They do exist.  Many work as
+contractors.   Luckily, world-wide cooperation currently works
+well.
+
+### Q: Is SWI-Prolog a prototyping language?
+
+Yes and no.  Prolog is good at prototyping because the brevity of the
+code allows for exploring ideas quickly.  Prolog is also mature enough
+to bring your prototype to the next level and use the demonstrator to
+convince your customers or investors.  Many companies also proofed it
+to be suitable for running production software.  Note that the
+abstract and concise code that can be read and written by domain
+experts make this notably viable in domains where the rules change
+often.
+
+For programming in the large we have _modules_ to encapsulate the
+code as well as support for _testing_, _documentation_, _static
+analysis_, _coverage analysis_, _profiling_, etc.
+
+Still, companies may at some point decide that it is better to rewrite
+(part of) the application in another language.  Efficiency, experience
+of employees or uniformity of the technology stack may drive this
+decision.  SWI-Prolog allowed you to convince customers and investors
+and bring the system to the market early as well as to fully grasp the
+desired functionality and required algorithms.  Rewriting is now much
+easier.  Note that the good integration between SWI-Prolog and many
+other languages allows for migrating gradually.
+
+### Q: How is SWI-Prolog integrated in our IT infrastructure?
+
+There are roughly two ways.  One option is to connect SWI-Prolog
+through some standard protocol.  Readily available is to use HTTP
+(including WebSockets), STOMP (connects to e.g, RabbitMQ), Redis and
+ROS2 (Robotics Operating System).  SWI-Prolog can read and write XML,
+JSON, YAML, Google's protocol buffers (protobuf), RDF (ntriples,
+Turtle, RDF/XML).  Contact us if you need support for another
+protocol.
+
+Alternatively, SWI-Prolog can be embedded in a program written in some
+other language.  We provide this feature for a large range of
+languages, e.g., C, C++, Java, Rust, JavaScript and Python.  This is
+often easier to achieve.  Languages without preemptive multi-threading
+support such as JavaScript and Python do pose challenges when dealing
+with threaded applications.
+
+### Q: What are the deployment options?
+
+SWI-Prolog applications may be deployed in many different ways.  _In
+house_ deployment may focus on easy debugging and updates.  End user
+products may prefer a single file executable without dependencies that
+make it hard for the end user to extract details about the algorithms
+used.
+
+A SWI-Prolog process consists of the runtime system that is by default
+packaged as a shared object (DLL) and the Prolog code.  The Prolog
+code can be distributed as _source_ or _virtual machine code_ (similar
+to e.g., Java ``.class`` and ``.jar`` files).  The _virtual machine code_
+may just be for your application or represent the entire program.  The
+first is called a _quick load file_ and the second a _saved state_.  A
+_state_ can be distributed as a file or embedded in a shared object or
+executable.  Code may be _obfuscated_, which implies that internal
+identifiers are replaced by generated constants and debug information
+such as source code locations are not included.  Finally, it is
+possible to add arbitrary (data) files to the _state_.  Depending on
+the OS, it is possible to distribute arbitrary complex applications as
+a single file, possibly statically linked, executable.
+
+### Q: What about the security of my SWI-Prolog application?
+
+Security is now a big issue.  Being a niche language, there are few
+tools available to access the security of Prolog programs.  Written in
+C, the security of SWI-Prolog itself has gone through auditing
+processes several times.  A couple of issues have been fixed as a
+result of this.  Given a secure Prolog implementation, security of
+applications written in this Prolog comes cheap.  Prolog memory
+handling is safe, so _buffer overflows_ are not possible.  _Injection
+attacks_ are possible.  The design of relevant libraries as well as
+the support for _quasi quotations_ avoid the need for managing data
+that satisfies some formal syntax as text (using strings).  Almost all
+manipulation or generation of such data is performed by parsing and
+manipulating the AST or generating the AST from scratch followed by
+generating the text from the AST.  A noteworthy example is the
+framework for generating HTML which makes it impossible to generate
+invalid HTML.  Eventually we had to add an escape mechanism to inserts
+text literally because customers had client software that insisted on
+specific, invalid, HTML content.
+
+
+### Q: What does SWI-Prolog has to offer for maintenance and debugging?
+
+  - A graphical source level debugger
+  - Dynamically configurable debug log messages and _assertions_
+  - Profiling and coverage analysis
+  - Unit testing.  Tests may be run in parallel.
+  - A built-in Emacs clone, the [sweep mode](https://eshelyaron.com/sweep.html)
+    for GNU Emacs and several externally available modes for vscode,
+	Eclipse and more.
+  - Reliable hot swap of code, even on active multi-threaded server
+    processes.  This allows for adding debug log statements without
+	down time as well as hot fixing of issues without down time.
+  - _Secure login_ to Prolog processes using SSH.   This allows for
+    inspecting the state of services or embedded Prolog instances
+	as well as interactive testing and using the hot swap facilities
+	to investigate and fix bugs.
+
+### Q: How portable is SWI-Prolog?
+
+SWI-Prolog is written in C, following the C11 standard.  It may be
+compiled using gcc or clang.  It does not use any assembly code.  It
+does use gcc and clang _built-in functions_, notably for lock-free
+thread synchronization using the _atomic_ built-ins and for fast but
+safe arithmetic using the overflow checking arithmetic built-ins.
+
+It can also be compiled using the Microsoft MSVC but, lacking some
+extensions, this version is considerably slower.  It supports both 32
+and 64 bit architectures on a wide range of CPUs.  All CPUs supported
+by [Debian
+Linux](https://www.debian.org/releases/stable/i386/ch02s01.en.html)
+are supported. Low level OS access is provided for POSIX based systems
+(Linux, *BSD (including MacOS) and Windows.  Finally, there is a
+[WASM](https://webassembly.org/) based version that can run in your
+browser or under Node.js.  It is available as [npm
+package](https://www.npmjs.com/package/swipl-wasm).
+
+Practically all features are transparently supported on all supported
+platforms.  For all platforms SWI-Prolog comes with small extensions
+to access functionality that is platform specific and cannot be
+generalized such as accessing the browser DOM from the WASM version.
+
+
+### Q: Licenses, open source ...
+
+#### Q: What are the license conditions for SWI-Prolog?
+
+SWI-Prolog is distributed under the permissive BSD-2 license.
+All software that is part of the standard distribution is either
+covered by this license, concerns external code covered by one
+of the other permissive licenses (BSD-3, MIT, Apache-2) or is
+optional.  Optional components covered by GNU licenses are
+
+ - The GPL licensed [readline](https://tiswww.case.edu/php/chet/readline/rltop.html)
+   Command line editor.  This interface may be loaded on demand
+   to provide a better interactive experience.   The default is
+   to use the BSD [libedit](https://www.thrysoee.dk/editline/)
+   Finished applications rarely need either.
+ - The LGPL licensed [GMP](https://gmplib.org/) library provides
+   unbounded integers and rational number support.  This is the
+   default.  Alternatively we provide equivalent functionality
+   by means of [LibBF](https://bellard.org/libbf/) under the MIT
+   license.   The LibBF version is smaller but slower.
+
+#### Q: Why is SWI-Prolog open source?
+
+SWI-Prolog is further developed and maintained by SWI-Prolog Solutions
+b.v. under the permissive open source BSD-2 license terms.  We
+strongly believe that open source is the best model for infrastructure
+such as SWI-Prolog because
+
+  1. Open source allows users to assemble their own configuration on their
+     own environment.  Users have been the driving force for many
+	 of the available ports.
+  2. Open source simplifies debugging, notably when embedding Prolog
+     or using foreign language extensions.
+  3. Open source allows for ports, fixes and changes without having
+     to rely on a vendor.  Depending businesses can hire anyone to
+	 solve their problem or acquire the expertise to do so in house.
+  4. More eyes find more bugs.  This has been said many times.  In
+     our experience it is true, but it requires a long time to
+	 establish a community with enough expertise to make it true.
+	 SWI-Prolog has that community.
+  5. Open source simplifies growing the user community.  A large
+     user community makes it easier to find programmers and get
+	 answers to your problems.
+  6. Open sources comes with much lower cost for sales and
+     distribution.
+  7. Open source provides direct communication between users and
+     developers.  You can share your problems and the
+	 community can come up with suggestions or ways to resolve
+	 your problems.
+
+
+#### Q: What about vendor lock-in?
+
+The core of Prolog is standardized by ISO/IEC 13211-1:1995.
+SWI-Prolog deviates from this standard on several points, notably
+preferring integer and rational number arithmetic over using floating
+point numbers, provide support for Unicode programs and reinterpret
+some syntactic constructs to allow for _dicts_ as primary citizens.
+Programs that avoid some edge cases run unmodified on a large number
+of Prolog implementations.
+
+Although the Prolog standard for modules was never adopted, a good
+number of implementations support the module system introduced by
+Quintus Prolog.  While most systems extended this module system,
+basic usage suffices for many applications and is portable.
+
+Several extensions are widely adopted, notably _unbounded integer
+support_, _constraints_ (_attributed variables_) and _tabling_.
+
+In addition to this, SWI-Prolog has several fairly unique extensions.
+Examples are mature multi-threading support, _delimited
+continuations_, _engines_, (database) _transactions_, _rational
+numbers_, _string_ and _dict_ data types.  Availability of the sources
+under the BSD-2 license and a large and active community is your
+warrant here.  The resources required to maintain SWI-Prolog or port
+required features to another target system should be manageable for
+most commercial users.
+
+In general, porting to another implementation that satisfies the
+requirements of your application is non-trivial but requires only a
+tiny amount of resources compared to the initial development.  The
+permissive license of SWI-Prolog allows porting libraries rather than
+reimplementing them if they do not exist on the target platform.
+
+
+## What does SWI-Prolog Solutions b.v. offer?
+
+### O: Access whether SWI-Prolog is suitable for your problem
+
+Can SWI-Prolog  solve your problem?  How  can it do so?   What are the
+risks involved?  Does it scale?  How do we interface with our existing
+infrastructure?  (Where) can we find programmers?
+
+We are happy to discuss your case.  For several customers we developed
+a _proof of concept_ (POC).
+
+
+### O: Help with design and implementation
+
+Our involvement  may continue by  providing support in the  design and
+implementing the complicated modules of the design.  A common split of
+responsibilities is  for you to  provide the domain  knowledge (rules)
+and for SWI-Prolog Solutions b.v. to  provide the tooling to make them
+work.  Your  business remains  in control  while outsourcing  the hard
+work.
+
+### O: Provide education and training
+
+SWI-Prolog is a rich environment.   While basic Prolog is well covered
+in many  books, there is little  public information on how  one should
+use  Prolog  in professional  environments.   We  offer training  that
+addresses your specific problems, including code reviews.
+
+### O: If needed, extend or improve SWI-Prolog
+
+The most  common improvement  we supply  are interfaces  to languages,
+protocols, data  formats, etc.   We also provide  tooling such  as for
+additional static analysis, documentation and testing.  We can provide
+language extensions,  improved performance, better deployment  if your
+product needs this.
+
+### O: Provide support for SWI-Prolog
+
+At this moment we do not provide support contracts you can simply
+subscribe too.  From the [Discourse
+forum](https://swi-prolog.discourse.group/) and [GitHub
+issues](https://github.com/SWI-Prolog/swipl-devel/issues) you will
+learn that problems are typically addressed quickly.  We are happy to
+discuss a support contract with you to address your specific needs.
+
+### Q: Where do I contact SWI-Prolog Solutions b.v?
+
+Please send an email to
+[solutions@swi-prolog.com](<mailto:solutions@swi-prolog.com>)
+
+### Q: How is SWI-Prolog Solutions b.v. organized?
+
+SWI-Prolog Solutions b.v. is a company registered in the Netherlands
+with the Chamber of commerce (KvK) number 80154573.  A "b.v." is a
+Dutch _private limited company_.
+
+
+## SWI-Prolog Solutions b.v. seeks cooperation with big companies and big projects
+
+SWI-Prolog solutions b.v. is interested in cooperation in big projects
+that can spin enough resources to speed up development or provide long
+term  guaranteed sustainable  development and  maintenance.  We  offer
+close cooperation with developers, priority  for your needs in further
+system  development  and  training.   People  cooperating  in  such  a
+cooperation may be employed by SWI-Prolog Solutions b.v., but can also
+be employees of  your business or work as contractors.   Our aim is to
+enlarge  the  group  of  people that  are  dedicated  to  SWI-Prolog's
+development.  Your benefit is access to sustainable high valued Prolog
+implementation with the flexibility offered by in-house development at
+lower cost and with higher impact.
diff --git a/commercial/index.txt b/commercial/index.txt
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-# Using SWI-Prolog for commercial applications
-
-SWI-Prolog is being used for commercial applications. The [license
-conditions](</license.html>) allow for embedding in commercial
-applications without restrictions on the license conditions for the
-proprietary code.
-
-We welcome commercial usage of the system.  Commercial users have
-had a major impact on the system by sponsoring the
-development.  Examples of *sponsored* features and components are:
-
-  - The initial garbage collector
-  - Unbound integer and rational number support
-  - The [PlDoc](</pldoc/package/pldoc.html>) documentation system
-  - The [PlUnit](</pldoc/package/plunit.html>) testing system
-  - The [SSL](</pldoc/package/ssl.html>) interface
-  - Redesign of the (stack) memory management to avoid using
-    the C stack for recursive traversal of Prolog terms, make
-    threads more memory efficient and remove the limitation of
-    the number of threads.
-
-Commercial users have greatly helped in *debugging* several features,
-notably multi-threading support and the
-[ODBC](</pldoc/package/odbc.html>) interface.
-
-Finally, commercial users have *provided packages*.  While making your
-package available requires an investment, you get a pay-back because
-others will help you to debug it and clean the interfaces.  Examples of
-such packages are:
-
-  - The [JPL](</packages/jpl/>) Java interface.
-  - The [TIPC](</pldoc/package/tipc.html>) networking interface.
-  - The [Google protocol buffers](</pldoc/package/protobufs.html>)
-    interface.
-  - The [CQL](</pldoc/man?section=cql>) library
-
-Involvement of commercial users is vital to the project!