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 A simple set of basic routines for working with a 3x3x3 Rubik's Cube.
 
 Work in progress.
+
+## How to use CubeCore
+
+TODO
+
+## The cube
+
+Each piece is represented by an (unsigned) 8-bit integer. The 4
+least-significant bits determine which piece it is, the other 4 determine
+the orientation.
+
+Edges are numbered as follows (see also cube.c):
+UF=0 UB=1 DB=2 DF=3 UR=4 UL=5 DL=6 DR=7 FR=8 FL=9 BL=10 BR=11
+
+Corners are numbered as follows:
+UFR=0 UBL=1 DFL=2 DBR=3 UFL=4 UBR=5 DFR=6 DBL=7
+
+The orientation of the edges is with respect to F/B, the orientation of
+corners is with respect to U/D.
+
+The permutation of the center pieces is not stored. This means that the
+cube is assumed to be in a fixed orientation.
+
+## I/O format
+
+Reading and writing is not done directly via stdin / stdout, but via an
+array of char (called buf in the prototypes below).
+
+Multiple representations of the cube as text are supported:
+
+- H48: a human-readable format.
+  Each edge is represented by two letters denoting the sides it
+  belongs to and one number denoting its orientation (0 oriented, 1
+  mis-oriented). Similarly, each corner is represented by three letters and
+  a number (0 oriented, 1 twisted clockwise, 2 twisted counter-clockwise).
+
+  The solved cube looks like this:
+
+  UF0 UB0 DB0 DF0 UR0 UL0 DL0 DR0 FR0 FL0 BL0 BR0
+  UFR0 UBL0 DFL0 DBR0 UFL0 UBR0 DFR0 DBL0
+
+  The cube after the moves R'U'F looks like this:
+
+  FL1 BR0 DB0 UR1 UF0 UB0 DL0 FR0 UL1 DF1 BL0 DR0
+  UBL1 DBR1 UFR2 DFR2 DFL2 UBL2 UFL2 DBL0
+
+  Whitespace (including newlines) between pieces is ignored when reading the
+  cube. A single whitespace character is added between pieces when writing.
+
+- SRC: format used to generate code for internal use.
+  If OUT is the output in SRC format, one can use `cube_t cube = OUT` to
+  declare a new cube object.
+
+- LST: a format for internal use and generating code.
+  The cube is printed as a comma-separated list of 20 integers, as they appear
+  in cube_t. Corners come first, followed by edge (unlike H48).