Equation (18) in p. 3

$DD=(1+B¯)λ-(1-rρ)·B¯·λ1-B¯B¯$
(18)

Should be:

$DD=(1+B¯)λ-(1-rρ)·B¯·λB¯-1B¯$
(18)

Note the change of sign of the exponent in the last coefficient — it must be changed from

$(1-B)/B$

to

$(B-1)/B$

as shown in the second equation above.