What is the significance of Index 1, 2 and 3 in FAST(MIN) and SLOW(MAX) libraries ?

[nee.sarathi]

What is the significance of Index 1, 2 and 3 in FAST(MIN) AND SLOW(MAX) Libraries of a Asic physical design Timing Libraries? An example of Fast.lib file script as following

power_lut_template(energy_template_7x3x3) {
variable_1 : input_transition_time;
variable_2 : total_output_net_capacitance;
variable_3 : equal_or_opposite_output_net_capacitance;
index_1 ("1000, 1001, 1002, 1003, 1004, 1005, 1006");
index_2 ("1000, 1001, 1002");
index_3 ("1000, 1001, 1002");
}

internal_power() {
related_pin : "A";
equal_or_opposite_output : "CO";
when : "!B & CI";
rise_power(energy_template_7x3x3) {
index_1 ("0.025, 0.08, 0.3, 0.7, 1.2, 1.7, 2.3");
index_2 ("0.00035, 0.084, 0.3115");
index_3 ("0.00035, 0.084, 0.3115");
values ( \
"0.173616, 0.181588, 0.172883", "0.183229, 0.177195, 0.168596", "0.183029, 0.179954, 0.168337", \
"0.180228, 0.188447, 0.179809", "0.188010, 0.180779, 0.172115", "0.187822, 0.183594, 0.171892", \
"0.200983, 0.207213, 0.198544", "0.207683, 0.206038, 0.197350", "0.207523, 0.208829, 0.197092", \
"0.261798, 0.258727, 0.249867", "0.261760, 0.254885, 0.246014", "0.261507, 0.257729, 0.245796", \
"0.335059, 0.328048, 0.319285", "0.331383, 0.324283, 0.315217", "0.331255, 0.327110, 0.314977", \
"0.400351, 0.394636, 0.385639", "0.396517, 0.391657, 0.382612", "0.396351, 0.394559, 0.382403", \
"0.483432, 0.476348, 0.467797", "0.478057, 0.474737, 0.465572", "0.477734, 0.477538, 0.465257");
}

Can aaaaany budy help me?