Cache Reference memory matrix

Can some one please tell me who the rules of the matrix work? Im not understanding this format

Cache memory systems 103 Line references 0 0 RO2 R1 R2 R3 0 Register stack Least recently used line from algorithm (a) Register stack method Line relerences 3 O 31 0031 1 1310 1 1/3 11/311 1 0 211 311 0 0 210 21 0 210 2 00 20 0 211 1 10 0123 01 23 0123 0123 0123 01 23 012 3 2 0 Least recently used line from algorithm (b) Reference matrix method