The stationarity conditions for an autoregressive (AR) process in
general are reduced to a remarkably simple inequality if the lag
coefficients are restricted to be identical. The condition is not only
analytically elegant but also applicable in checking the validity of the
stationarity conditions for such a restricted AR process of any order.We are deeply indebted to Professor Paolo
Paruolo, NP co-editor of Econometric Theory, and anonymous
referees for constructive comments and suggestions that led to significant
improvements. Errors, if any, are solely ours.