CMP.2:4.1 - Fix the question and the available operations

Describe an input x, the information available about it, and what a returned answer must allow its recipient to do. Asking for an optimum value, one attaining object, or every attaining object gives different result requirements. State the empty and degenerate cases when they belong to the input family.

List the operations that can actually be performed on this input: inspect a constructor, split an interval, compare keys, compute a remainder, test a condition, or call a supplied procedure. A proposed step such as “choose the correct partition” remains a construction task until the partition can be obtained.

For example, maximum segment sum on a sequence of integers asks for a contiguous nonempty segment with largest sum. Returning its sum answers a value query; locating the segment also requires endpoints. Permitting the empty segment changes the base case and the answer on an all-negative input.