## KDB+, Elm and web sockets

July 15, 2014

In the KDB+ implementation of the Conway’s Game of Life that I presented in my previous post there was one element missing – a GUI that would display the results of the simulation. Since I have been planning to have a look at Elm for a while, I checked if I can set up KDB+ talking to an Elm application and it turned out it is very easy to do – with web sockets.

Elm is a functional programming language that compiles to HTML, JavaScript and CSS code intended to run in a browser. The declared paradigm for Elm is Functional Reactive Programming. FRP is not exactly what it used to be back in the days of Conal Elliot and Paul Hudak’s original work. It is now more of a buzzword covering more and more semantic area. The key concept in the  Elm’s take on FRP are signals. A Signal a type in Elm represents a value of type a that changes in time. Signals can be thought of as streams of discrete events carrying values. They can be combined, filtered, counted and so on. Ultimately we obtain a value of type Signal Element that can be displayed in the browser (possibly in a div if one embeds an Elm application this way). The Elm site contains a very convincing argument on why all this is a good idea.

## Game of Life with Enterprise Components

May 20, 2014

DEVnet (the company I work for) has decided to release one of its products – Enterprise Components (called EC below) – as free software. Since I contributed some code to it I would like to advertise it a bit on this blog.

## What are Enterprise Components?

EC is a collection of libraries and tools that support building systems based on KDB+ – a database made by Kx Systems. Traditionally KDB+ has been mostly used for time series analytics in finance industry. Part of the reason for that was that the commercial license for KDB+ was very expensive. However, some two months ago Kx announced that they now allow commercial use of the free-of-cost 32-bit version of their product. This opened a path for KDB+ applications in areas well beyond institutions with deep pockets.

The main limitation of the 32-bit version is the amount of data it can handle – about 1GB. This limitation is per-process though and since KDB+ has a built-in inter-process communication protocol one can create very capable systems using the free version just running as many instances as needed.

Enterprise Components can be thought of as a layer above KDB+. EC provide logging, process management, configuration management, user access control, system monitoring and more – all that is needed if you want to build a larger scale system. Typical use cases are covered in the standard components provided with EC so that one can define a basic system with data feeds, in-memory database backed by on-disk journals and storage and archiving at the end of day with configuration only.

## ProofPeer

February 1, 2014

ProofPeer is a project to create a cloud-based social network interactive theorem proving system. I wrote about it a year ago. The project looked dormant since about July, but now it got funding and is accepting PhD studentship applications.

## Proof market

January 11, 2014

Yoichi Hirai has created a site where one can submit bounties for proofs of theorems in Coq formal proof management system.  Currently the bounties are sent to a Bitcoin address that is under the control of the site owner. This requires of course  some trust in the site owner, although reducing the trust requirements is under discussion. I don’t think it is possible to implement a Coq checker in Script though (as Yoichi suggests) as Script is not Turing complete. Something like what is described in the Using external state chapter of the Bitcoin wiki page on contracts is more realistic.

There are currently bounties for proving False (i.e showing inconsistency of Coq) and a couple of theorems that seem quite involved. The funny thing is proving False is also on the list of solved problems. Someone has earned 0.999 BTC by submitting four lines that just change the meaning of False and state a trivial theorem using that changed meaning, thus showing Pollack-inconsistency of Coq.

## Bitcoin epic fails

January 4, 2014

Bitcoin, or more generally cryptocurrencies  is  a somewhat complex subject in that it connects technology, economics and law. But it is kind of fashionable now, so some famous people decide to publicly formulate opinions about it without devoting time and effort to gain knowledge about how the technology actually works. As one commenter on the Marginal Revolution site nicely put it:

The situation has all the makings of your standard paradigm shift, where pundits with less neurological plasticity give future history books lots of look-how-wrong-they-were quotes.
I would like to mention two examples of such epic fails.

## IsarMathLib version 1.9.1 released

January 3, 2014

This is a maintenance release mostly to update IsarMathLib to Isabelle 2013-2. The RIPEMD-160 hash (a2ef972973bb2d072c7702d28dcfabee9026bd3b) of the proof document for this release is timestamped in the Bitcoin blockchain at 1FrXV7eifF2zruVr8YHJdvV8GHucUAqxYy.

## Java, Mockito and ArgumentCaptor

September 3, 2013

I knew that day would come at some point. I am programming in Java. One thing that took me longer that I think it should was to figure out how to use Mockito‘s ArgumentCaptor to verify arguments with which methods are called. In this post I share some code snippets that do that, for my reference and hopefully to help other Java beginners.

## IsarMathLib 1.9.0 released

July 26, 2013

I have released version 1.9.0 of IsarMathLib. This is a quite large release with 10 new theory files and 155 new theorems, all contributed by Daniel de la Concepción Sáez. The first of the files contributed by Daniel (released in 1.8.0), Topology_ZF_4 about nets, filters and convergence in topological spaces is now presented on the isarmathlib.org site. The rest of Daniel’s contributions for now can be viewed in the proof document and the outline.

Here is a short description of what is in the new theories:

## Gowers and Ganesalingam

May 12, 2013

There is a series of posts at the Timothy Gowers’s blog about software that can “solve mathematical problems” which he has been working on with Mohan Ganesalingam for the last three years. The word “problems” is used here in the way a mathematician would use it – it’s really about software that can support a mathematician trying to write a proof of a theorem. The goal is for the program to write proofs that look like ones produced by a human. The experiment Gowers sets up on his blog presents several theorems with proofs written by two humans (an undergraduate and a graduate student) and one created by the program and asks the readers to guess which proofs are written  by whom. The results are truly remarkable – while I, and most of the audience, could have a good guess which proof is written by the software, I believe I could guess it only because I had known one of the three proofs was such. If a student submitted such proof as homework to me, I would have no suspicion at all.

## IsarMathLib 1.8.0 released

February 25, 2013

I have released the 1.8.0 version of IsarMathLib. This version works with the new Isabelle2013 (released about two weeks ago). The new material in this release mostly comes from contributions by Daniel de la Concepción Sáez, who added 5 theory files with about a hundred theorems about general topology. The subjects range from convergence of nets and filters and related continuity properties of functions, through some generalized notions of compactness and connectedness, to rather abstract (like, category theory abstract) subjects of heredity and spectra of topological properties. Unfortunately, it will take some time before those theories will be presented on the FormalMath.org site, as my parser is not good enough to parse Daniel’s advanced Isar style.  I will work on this though and in the meantime an interested reader can have a look at the Isabelle generated full proof document or the outline.

As for myself, I have finished the proof that the function $(x_0, x_1,...,x_{n-1})\mapsto \sum_{i=0}^{n-1}x_i$ is continuous in the natural topology on the space of $n$-element sequences of a topological group.