L2enableustoapplyagainthisideafornonabelianIwasawatheory.Inthiscircleofideas,thisarticleisdevotedtothefirstpartofastrategyofprovingadivisibilitytowardsaMainConjecture”`alaIwasawa”asitisannouncedin[19]fortheSelmergroupofatwovariableadjointmodularGaloisrepresentationbyusingcongruencesbetweencuspidalSiegelmodularforms...