The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the protocol is incentive-compatible and secure against colluding minority groups, i.e., it incentivizes miners to follow the protocol as prescribed.

We show that the Bitcoin protocol is not incentive-compatible. We present an attack with which colluding miners obtain a revenue larger than their fair share. This attack can have signi cant consequences for Bitcoin: Rational miners will prefer to join the sel sh miners, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency.

Här bjuder RiotMinds på ett stycke svensk rollspelshistoria! Först tänkte vi: Det som har varit, har varit! Sen tänkte vi: Varför inte? Och därför väljer vi nu att, som i ett led av det stora 30-årsjubileumet, släppa Drakar och Demoners historia fritt.

Object-oriented programming has worked quite well – so far. [...] However, objects can deceive us. They can lure us into a false sense of understanding.


This article discusses two examples, a Pacman game and a soccer simulation where antiobjects are employed as part of a game AI called Collaborative Diffusion. In Collaborative-Diffusion based soccer the player and grass tile agents are antiobjects. Counter to the intuition of most programmers the grass tile agents, on top of which all the players are moving, are doing the vast majority of the computation, while the soccer player agents are doing almost no computation. This article illustrates that this role reversal is not only a different way to look at objects but, for instance, in the case with Collaborative Diffusion, is simple to implement, incremental in nature and more robust than traditional approaches.

Jouyou kanji (常用漢字) is the set of 1945 kanji that the Japanese Ministry of Education has decided that school children must learn. We have compiled a list of the about thousand kanji that Japanese children learn from first to sixth grade. These first 1006 kanji are also called the Kyouiku kanji.

The following practise sheets are made to have the left part folded to cover the actual kanji, so you will have to remember the kanji, and not just copy it mechanically. If you are unsure of the stroke order, please use the kanji dictionary found on the right hand side of this site. Most kanji have stroke order diagrams attached.

Non-myth #4: Programming is asocial.

Yes, but it depends what you mean by asocial. It is true that a programmer spends long hours by herself in front of a computer screen, although there are also meetings with team members and customers. There certainly are “social” professions where you are in constant contact with other people. The problem is that in most cases the human contact is superficial and asymmetrical, because you don't “chat” with your “clients.” You may not even want to develop a warm relationship with your clients, for example, if you are a police detective interrogating hardened criminals.


It is reasonable for Tiffany to choose to become a social worker because she likes helping people directly, but she must remember that she will not become a friend to her clients.

More than 15 years ago Russian scientist Kirill Yeskov tried to settle certain geographical problems in Tolkien's fantasy world. One thing led to another, and he tackled a bigger project - what if we assumed that it's no less real than our world? His conclusion was that in such a case, the story of the Ring of Power is most likely a much-altered heroic retelling of a major war - but what was that war really about?


I was impressed enough by this work to spend a few dozen lunch hours translating it to English. [...] I now offer this work for your perusal.

On Lisp is a comprehensive study of advanced Lisp techniques, with bottom-up programming as the unifying theme. It gives the first complete description of macros and macro applications. The book also covers important subjects related to bottom-up programming, including functional programming, rapid prototyping, interactive development, and embedded languages. The final chapter takes a deeper look at object-oriented programming than previous Lisp books, showing the step-by-step construction of a working model of the Common Lisp Object System (CLOS).

As well as an indispensable reference, On Lisp is a source of software. Its examples form a library of functions and macros that readers will be able to use in their own Lisp programs.

I remember using this handy cheat sheet for Emacs -- or something extremely similar to this -- in 1989. Even in the computer industry, there are some things that don't change that quickly.

The onset of summer is no excuse to stop learning. In this year’s session, we will address Quantum Physics. Be here each Monday morning through July and August for a new lesson in the nine part series, covering graduate level physics concepts with grade school math, or no math at all. The first lesson: Classical Thinking: Why Does It Fail?

It is common to argue that intellectual property in the form of copyright and patent is necessary for the innovation and creation of ideas and inventions such as machines, drugs, computer software, books, music, literature and movies. In fact intellectual property is a government grant of a costly and dangerous private monopoly over ideas. We show through theory and example that intellectual monopoly is not necessary for innovation and as a practical matter is damaging to growth, prosperity and liberty.

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