I am currently learning about time series. Understand that in order to apply ARMA model, the time series must be stationary, which implies no trend, no cyclic pattern. Also I learnt that time series can be decomposed into seasonal, trend and white noise. so I would like to ask if the series can be decomposed into seasonal and trend, can it be still stationary? and what is the relation between decomposition and stationary? any insightful reply would be greatly appreciated.