@property<EOL><INDENT>def states(self):<DEDENT>
raise NotImplementedError<EOL>
Return the state space. Might include subdicts if multiple states are 
available simultaneously.

Returns:
    States specification, with the following attributes
        (required):
        - type: one of 'bool', 'int', 'float' (default: 'float').
        - shape: integer, or list/tuple of integers (required).