Algorithm 97: Shortest path

procedure arithmetic (a, b, c, op); integer a, b, c, op; onlment This procedure will perform different order arithmetic operations with b and c, putting the result in a. The order of the operation is given by op. For op = 1 addition is performed. For op = 2 multiplicaLion, repeated addition, is done. Beyond these the operations are non-commutative. For op = 3 exponentiation, repeated multiplication, is done, raising b to the power c. Beyond these the question of grouping is important. The innermost implied parentheses are at the right. The hyper-exponent is always c. For op = 4 tetration, repeated exponentiation, is done. For op = 5, 6, 7, etc., the procedure performs pentation, hexation, heptation, etc., respectively. The routine was originally programmed in FORTRAN for the Control Data 160 desk-size computer. The original program was limited to tetration because subroutine recursiveness in Control Data 160 FORTRAN has been held down to four levels in the interests of economy.