Diagrams

A rule's diagram shows how things are arranged. Let's look at a rule more closely:

@ => _
_    @

Inputs: The @ symbol shows where the atom is. The _ symbol checks for an empty space. In other words, the rule checks if there is an empty space below the atom.

Outputs: The @ symbol shows where to put the atom. The _ symbol shows where to put an empty space. In other words, the rule moves the atom down, leaving an empty space behind.