Algorithm 18.1 outlines the procedure for searching a non-dense multilevel primary index to retrieve a file record. Adapt the algorithm for each of the following cases:
a. A multilevel secondary index on a non-key non ordering field of a file. Assume that option 3 of Section 18.1.3 is used, where an extra level of indirection stores pointers to the individual records with the corresponding index field value.
b. A multilevel secondary index on a non-ordering key field of a file.
c. A multilevel clustering index on a non-key ordering field of a file.