docs: def is_contradictory(self, other):
          """
          Can these two strings coexist ?
          """
          other = StringCell.coerce(other)
  
          if self.value is None or other.value is None:
              # None = empty, and won't contradict anything
              return False
  
          def sequence_in(s1, s2):
              """Does `s1` appear in sequence in `s2`?"""
              return bool(re.search(".*".join(s1), s2))
  
          return not sequence_in(self.value, other.value) and \
              not sequence_in(other.value, self.value)