arXiv:hep-ph9803328v1 12 Mar 1998UCL-IPT-98-04Hadronic Phases and Isospin Amplitudes in D(B)→ππ andD(B)→KˉK DecaysJ.-M. G′ erard J. Pestieau and J. WeyersInstitut de Physique Th′ eoriqueUniversit′ e