Update README.md

README.md

@@ -15,6 +15,44 @@ if we look at clean the cube, we see 6*9 facelets.
 
 ![](http://www.kociemba.org/pics/cubeclean.gif)
 
+## Cube string notation
+The names of the facelet positions of the cube (letters stand for Up, Left, Front, Right, Back, and Down):
+```
+             |************|
+             |*U1**U2**U3*|
+             |************|
+             |*U4**U5**U6*|
+             |************|
+             |*U7**U8**U9*|
+             |************|
+ ************|************|************|************
+ *L1**L2**L3*|*F1**F2**F3*|*R1**R2**R3*|*B1**B2**B3*
+ ************|************|************|************
+ *L4**L5**L6*|*F4**F5**F6*|*R4**R5**R6*|*B4**B5**B6*
+ ************|************|************|************
+ *L7**L8**L9*|*F7**F8**F9*|*R7**R8**R9*|*B7**B8**B9*
+ ************|************|************|************
+             |************|
+             |*D1**D2**D3*|
+             |************|
+             |*D4**D5**D6*|
+             |************|
+             |*D7**D8**D9*|
+             |************|
+```
+A cube definition string "UBL..." means that in position U1 we have the U-color, in position U2 we have the
+B-color, in position U3 we have the L color etc. according to the order `U1`, `U2`, `U3`, `U4`, `U5`, `U6`, `U7`, `U8`, `U9`, `R1`, `R2`,
+`R3`, `R4`, `R5`, `R6`, `R7`, `R8`, `R9`, `F1`, `F2`, `F3`, `F4`, `F5`, `F6`, `F7`, `F8`, `F9`, `D1`, `D2`, `D3`, `D4`, `D5`, `D6`, `D7`, `D8`, `D9`, `L1`, `L2`, `L3`, `L4`,
+`L5`, `L6`, `L7`, `L8`, `L9`, `B1`, `B2`, `B3`, `B4`, `B5`, `B6`, `B7`, `B8`, `B9`.
+
+So, for example, a definition of a solved cube would be `UUUUUUUUURRRRRRRRRFFFFFFFFFDDDDDDDDDLLLLLLLLLBBBBBBBBB`
+Solution string consists of space-separated parts, each of them represents a single move:
+* A single letter by itself means to turn that face clockwise 90 degrees.
+* A letter followed by an apostrophe means to turn that face counterclockwise 90 degrees.
+* A letter with the number 2 after it means to turn that face 180 degrees.
+e.g. **`R U R’ U R U2 R’ U`**
+
+
 
 ![Shuffled](https://user-images.githubusercontent.com/81550376/226800512-99b89e57-51f7-4a01-8829-9a9ff87f51a7.png)