WARN: This is a temporary fix that prevents the parser from crashing in the following faulty condition:
WARN: This is a temporary fix that prevents the parser from crashing in the following faulty condition:

  - M0 -> D1 is forbidden (*)
  - D0 -> D1 is not (whatever D0 means...)
  - D1 -> X2 is defined (where X is D or M)

This change may be discarded  in the very near future.

csb-toolbox/CSB