equation icon  -----gnn------ -gnn- angnn+1- an+1gnn+2- Rn = - bn + anRn+1 = - bn - . bn - . bn - ...., (127) n nn nn n+1 n n+2n Ln = - ----a-n------= - -an--.an--1gn .an--2gn-1 ..... (128) bnn + gnnLn -1 bnn- bnn-1- bnn-2-