Remarks on a technique of measuring CP phase alpha

We present a method to measure the CKM phase alpha and the tree and penguin (strong and electroweak) amplitudes in B-->pi pi decays, based on isospin consideration and the weak assumption that all tree amplitudes have a common strong phase and all penguin amplitudes have a different common phase. The method needs only the time-independent measurements of the relevant decay rates in B-->pi pi. We also propose a method to experimentally examine the validity of the assumption that all penguin amplitudes have the same strong phases, and to extract detailed informations about the hadronic matrix elements.