# PS6.5 for Example 6.4
open data6-3 
genr C1 = Cons(-1)
# print C1 to see how it is stored internally
print Cons C1
# generate DY(t) - DY(t-1) using the diff function 
genr DiffI = diff(DI)
# print DI and DiffI to see how they are stored internally 
print DI DiffI
# note that ols starts in 1949 because C1 and DiffI are 
# undefined for 1948 
ols Cons 0 C1 DiffI
