The user must write source files containing the arrays of functions which are the commands (cf. 5). The commands which are implemented in the library need not be redefined. Recall that there is one such array for each section !func of the initialization file, and the list of all such arrays must be given in the array proc (cf. 5). The user must also define the array Funcs of structures corresponding to numerical functions known by the expression evaluator (cf. 7), if the default one is not used.