Rubik’s cube is pretty simple, as you already know. So at first glance you may think there is little need, if any, to establish terminology. But before we start talking about the cube, we must decide on a common vocabulary, so that we can convey the information as intended. Terminology is important. And since I’m the one conveying the information in this series of articles, I’ll have to settle on terminology by myself. Here is what you need to know, in five easy paragraphs.
The cube is formed of smaller cubies. There exist only center, corner and edge cubies. A cube has 6 sides. Cubies can be swapped with each other, or flipped in place.
The cube sides are named T (top), L (left), F (front), R (right), B (bottom) and H (hidden). Whenever you turn the cube in your hands, the side you’re looking at is the front side, and so on. This means that any side can become the “top” side at any time.
A side rotation is just that – a rotation of the side. You can rotate a side clockwise or conter-clockwise. Also, you can rotate a side once, twice, or three times. If you rotate it more than three times, it’s just as if you had rotated it once, or twice, or three times, because four rotations bring the side back to its initial position. In other words, I might refer to a side rotation by saying “perform this rotation once, twice, or three times, and do it clockwise or counter-clockwise”.
I will set up a compact notation to talk about rotations. To rotate a side, I require the following information: the side to move, the direction of the rotation (clockwise or counter-clockwise) and the number of times I rotate. To represent the side under consideration, I will use its letter code. When referring to the direction of the rotation, I will append an apostrophe if the rotation is counter-clockwise. When referring to the number of times that the side rotates, I will append this number to the notation. Only if the number of rotations is not 1, will I append it. Here are a few examples:
- F3 – rotate the front side three times, clockwise.
- T’2 – rotate the top side twice, counter-clockwise.
- R – rotate the right side once, clockwise.
Finally, I introduce moves, which are just a collection of rotations. A move really is an indication to “apply the specified rotations in the given order”. F R F’ H3 is an example move, and it means “rotate the front side once clockwise, then rotate the right side once clockwise, then rotate the front side once counter-clockwise, then rotate the hidden (back) side three times clockwise”. Although each individual rotation can consider different top, front, bottom, left, right, hidden sides, a move always applies its rotations with the same top, front, bottom, left, right and hidden sides. Imagine what would happen if it were not for this restrictions… a move could then represent many different combinations, which makes no sense.
That’s it. Armed with terminology, we can start to refer to the cube and eventually solve it. Read on.