Section 6. 9 of your textbook ("debugging") lists three possibilities to consider if a function is not working.

The paced decision model is a tool that can be used in a variety of situationsit should clarify one's alternative and criteriapaced decision-making processused to solve problems in a rational, systematic way- state the problem- list the alternatives- identify criteria- evaluate alternatives- make a decisionstep 1 - problem: the first step is to state the problem. what car should i buy? step 2 - alternatives: list some likely alternativesstep 3 - criteria: the next step is to establish criteria - what is the most important to you. (these criteria need to be state din positive terms, i.e., stated as you what you want.) ex costs less than $4000; gets at least 25 mpg,; seats at least 4; has ac;   step 4 - evaluate each alternative by comparing it to criterion. if an alternative meets a criterion, pus a + in that box - if not put a -. at the end look to see which alternative meets your most important criteria. (some criteria will be more important than others. those may be given greater weight. and, if an alternative costs more than $4000, it probably won't matter if there is a + in all the other boxes.)step 5 - decide: based on the insights gained, make a choice. be sure to explain that it won't always be the one with the most +'s - since some criteria count more than othersthe strength of this tool lies in the ability of each student to determine their own criteria for evaluation