... generates a value of s from a value of y, and (20) generates a value of b from that value of s, there is an implicit function cali it F 1 that is defined by that interaction, generating that ... functional hierarchy expressed by the program requires the introduction of a non- numerical viz., boolean-valued variable. In general, variables in a program can be taken to range over any data ... (i) and (iii) each generates a value of a as a side effect !'~', a is generated by a subfunction, but not by the overall function , and b in (i) appears from nowhere !'~., as...