The following simple (but nonstandard) naming convention is used (see axes):

The SKI cube is a way of presenting a number of related calculi and logics which are obtainable from pure combinatory logic by one or more of three kinds of extension.
The origin of the cube is pure Combinatory Logic (c).
The three kinds of extension considered are called the axes of the cube.
The cube presents eight systems or kinds of system which are arranged at the vertices of the cube.
Those systems sharing a particular value on one of the dimensions of the cube are arranged around one of the faces of the cube.