Consider the following set of statements:

S1: A super key is a set of one or more attributes that, taken collectively, allows us to identify uniquely a tuple in the relation.

S2: If K is a super key, then so is any sub set of K.

S3: A referential integrity constraint requires that the values appearing in specified attributes of any tuple in the referencing relation also appear in specified attributes of at least one tuple in the referenced relation.

Which of the above statements is false?