First of all, what actually is a classic Rubik's cube?

Rubik's cube is a cube whose length is approximately 55 mm (2.2 in) in. It consists of 26 smaller cubes; one side is made up of 3x3 such cubes. If you take an ordinary cube and cut it as you would a Rubik's cube, you are left with 27 smaller cubes. You see, the inner smaller cube comes from the center of this cube, and this center is not contained in the Rubik's cube. In fact the smaller pieces of the Rubik's cube are not real cubes. We call such pieces cubies.

There are 6 cubies in the middle of individual sides, and those are rigidly interconnected by a six-armed spatial cross (they merely rotate around their axles). I will call those cubies centers. The cubies are connected to the cross by means of springs, thry cause other cubies to hold nicely togerther. Those center cubies have a colored sticker on their external sides, which determines the color of each face. The colors are usually white, red, blue, yellow, orange and green. Sometimes brown color replaces red color. The original Rubik's cube has coloring white opposite yellow, red opposite orange and blue opposite green. Yet another coloring, (widespread in America) exists: white opposite blue, red opposite orange and green opposite yellow. The former coloring has a certain logic, called "plus yellow," because opposite side of a primry color (white, red, blue) is formed by adding yellow color (yellow, orange, green). On the other hand, the latter coloring tries to combine opposite sides with maximum contrast.Each coloring can further have two variants due to mirror reflection. Those mutations are caused by the carelessness of the manufacturers, who pay attention to colors on opposite faces, but don't care if they are reversed. This is of great importance in creating three dimensional designs. This topic is discussed elsewhere.

We also have 12 edge cubies, or just edges. Those cubies have two stickers of different colors. All color combinations are exhausted, except those on opposite faces (that nakes sense; where would you put them….)

And the last type of cubies are eight corner cubies, or just corners. Those cubies have three differently-colored stickers on their mutually orthogonal sides.

1.2 Labelling of moves

As you surely know, the Rubik's cube has 6 sides.All sides can be rotated by a certain angle. This rotation is called a move. In order to be able to execute other moves, it is recommended to rotate by 0 (360), 90, 180, or -90 (270) degrees : - ). Of course, if you rotate a side, you rotate one third of the cube (9 cubies). This array is called a layer.

Having a cube in front of you, the individual layers are rotated thus:

• A layer facing towards you is the front layer, and is labelled as F (front).
• A layer facing away from you is the back layer and is labelld as B (back).
• A layer which is on top is the up layer and is labelled as U (up).
• A layer which is at bottom is the down layer and is labelled as D (down).
• A layer which is on your right is the right layer and is labelled as R (right).
• A layer which is on your left is the left layer and is labelled as L (left).

The move is labelled by the symbol of the layer you are turning (F, B, U, D, L, R). A symbol by itself labels a clockwise rotation of the layer. For a counterclockwise rotation,the layer symbol is followed by an apostrophe (a single quote}. For a 180-degree rotation, the layer symbol is followed by a numeral 2 or an exponent "to the second power." There are other ways of labelling the moves, but this one is the simplest and most widely used.

For a clearer understanding I offer an example:

F2 U' R

means: Rotate the front layer by a half-turn (180 degrees in any direction :- )), then rotate the up layer counterclockwise by a quarter-turn (90 degrees) and finally rotate the right layer clockwise by a quarter-turn.

It is worth noing, that you turn each side in a given direction, if the side is facing you (you don't need to pivot the whole cube, but rotate the side in the same direction you would rotate, if the side was facing you). It my not be completely clear at first, but it is sufficient, if you turn the cube so that the side to be manipulated is facing you, execute the move, and then turn the cube back to its original position.

I will indicate how I label the sides in a drawing of a given cube state:

fig. 1	fig. 2

Figure 1 shows the unsolved state of the cube, and figure 2 shows the solved state. The hidden sides of the cube may be seen, if mirrors are placed around the cube. Sometimes we will talk about correctly positioned corners/edges, correctly oriented corners and correctly reversed edges. A correctly positioned cubie is a corner or edge cubie that is at the right place on the cube relative to its centers. Correctly oriented corner is forther oriented so that the sticker of a given color is adjacent to the sricker of the center cubie of the same color. Correctly reversed edge is similar to a correctly oriented corner. A corner may be at the same place in three different orientations. An edge may be at the same place in teo different reversals.

Examples:

Correctly positioned and oriented corner	Correctly positioned and incorrectly oriented corner	Correctly positioned and oriented edge	Correctly positioned and incorrectly oriented edge

Certain corners and edges will be specified either by their colors (e. g. white-blue edge) or by their placement in the picture (e. g. UL edge) for edge common to the up and left layer.

That should be all for now. We will introduce more labelling in future chapters, depending on need.

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