code: def _unsigned_sub_overflow(state, a, b):
          
          cond = Operators.UGT(b, a)
          return cond
docs: Sign extend the value to 512 bits and check the result can be represented
           in 256. Following there is a 32 bit excerpt of this condition:
  
          a  -  b   ffffffff bfffffff 80000001 00000000 00000001 3ffffffff 7fffffff
          ffffffff     True     True     True    False     True     True     True
          bfffffff     True     True     True    False    False     True     True
          80000001     True     True     True    False    False     True     True
          00000000    False    False    False    False    False     True    False
          00000001     True    False    False    False    False     True    False
          ffffffff     True     True     True     True     True     True     True
          7fffffff     True     True     True    False    False     True    False