The square brackets to the left of the arrow indicate a single
phoneme or phone segment. The feature or features within the
brackets to the left of the arrow indicates the underlying representation or the structural description that must be satisfied for the given rule to apply. For example, rule (1) will apply to any segment that contains the feature (-sonorant) The square brackets to the right of the arrow indicate the value (s) that any feature (s) specified there must receive within the segments that meet the structural description. Therefore, rule (1) specifies that any segment that contains (-sonorant) will have a value of (+voiced).