a # 1 60 R 'r # n rowindices m;Lio                                      '
a # a,[1]  '"rowindices - first or last n rownumbers of matrix.         '
a # a,[1]  '"from ''the apl handbook of techniques'' copyright 1978, ibm. '
a # a,[1]  ' r#(r^=0)/r#nYI1YRm H Lio#1                                 '
Lfx a