taken to insure that the FVIM remains output set assignable. For the example problem, had x or y been chosen as the decision variable type, an output set assignment could not have been made. FVIM decisions may not be chosen so that the restrictions on FVIM outputs must be violated in assigning outputs. Consider the FVIM in Fig. 3-4 a). There are three function types and four variable types. Choosing x as the decision variable type results in the FVIM in Fig. 3-4 b) and choosing z results in Fig. 3-4 c). The FVIM in b) is not output set assignable according to the rules whereas the one in c) is. The decisions must be chosen so that there are the same number of variable type as function types with any given number of indices. 3.3.3 Index Outputs Index outputs are the outputs assigned in the Index Display Matrices. They indicate which of the variables of the output variable type will be the output for particular function index values. In extending index outputs from the IDM to a general solution procedure knowledge of the following properties is necessary. Theorem 3-1: All Index Display Matrices, when treated as incidence matrices are output set assignable provided they are not null. Proof: The proof is by induction and is divided into two parts, one for a list and one for a range. List: There must be at least one list element, which is an offset from the function index value. This is known from the definition of variable index lists. Therefore, for one function index value there is an output set assignment. Now suppose that there are output set assignments for an IDM with k rows. Row k+l introduces a new function index value, 1