Goal:
  
  ============================
   (None + Some 0 = None)


DEBUG:Going to execute:
reflexivity
Level 1: Backtrace:

In environment
z : Z
Unable to unify "Some z" with "Some z + Some 0".
Level 0: Backtrace:

In environment
z : Z
Unable to unify "Some z" with "Some z + Some 0".