@staticmethod
def char_sim(sc, tc, match_value=2, mismatch_cost=2):
    """
         Basic character similarity.
         @param  sc             source character
         @param  tc             target character
         @param  match_value    Score bump/reward if they match
         @param  mismatch_cost  Penalty if they don't match (should be non-negative)
         @return similarity between sc and tc
        """
    return match_value if sc == tc else -mismatch_cost
