Let \( R_1 = \{(a,b) \in N \times N : |a-b| \le 13\} \) and \( R_2 = \{(a,b) \in N \times N : |a-b| \ne 13\} \). Then on \( N \):
Both \( R_1 \) and \( R_2 \) are equivalence relations
Neither \( R_1 \) nor \( R_2 \) is an equivalence relation
\( R_1 \) is an equivalence relation but \( R_2 \) is not
\( R_1 \) is an equivalence relation but \( R_1 \) is not