//Given that
D = 1.5  //times wavelength

//Sample Problem 18-3a
printf("**Sample Problem 18-3a**\n")
deltaL = 0
printf("Waves undergo constructive interference at P1\n")

//Sample Problem 18-3b
printf("\n**Sample Problem 18-3b**\n")
deltaL = D
deltaPhi = 1.5*2*%pi
if modulo((deltaPhi/%pi), 2)==0 then
    printf("Waves undergo constructive interference at P2\n")
else
    printf("Waves undergo desstructive interference at P2")
end