Used to generate the Wold decomposition for the third model

Series[((1 - T B)/((1 - p B) (1 - B))), {B, 0, 
        10}]

Used to generate the Wold decomposition for the fourth model

Series[((1 - T1 B  - T2 (B^2) - T3 (B^3))/(((1 - B))^2)), {B, 0, 
        10}]