P=order
P=(lag, ..., lag ) ...(lag, ..., lag )
specifies the autoregressive part of the model. By default, no autoregressive parameters are fit.

P=(l , l , ..., l ) defines a model with autoregressive parameters at the specified lags. P= order is equivalent to P=(1, 2, ..., order).

A concatenation of parenthesized lists specifies a factored model. For example, P=(1,2,5)(6,12) specifies the autoregressive model