quantitaive analysis

Statement as per the book official GARP book (chapter 11, seasonal differencing): How is this equation MA(1)? Isnt this an MA(4) with theta=-1? And how is this covariance stationary? The characteristic equation is 1+z^4 with complex root of abs value of unity.

Not sure if i am missing something, but this seems to be contradictory. 1. Towards the end of page 126: "Adding a new variable to the model always increases the R2." 2. In the 2nd column on page 127: "As explained previously, adding an additional explanatory variable usually decreases R2 and...