  {We use the recent proof of Jacquet's conjecture due to Harris and Kudla, and
the Burger-Sarnak principle to give a proof about the relationship between the
existence of trilinear forms on representations of $GL_2(k_u)$ for a
non-Archimedean local field $k_u$ and local epsilon factors which was earlier
proved only in the odd residue characteristic by this author. The same method
gives a global proof of a theorem of Saito and Tunnell about characters of
$GL_2$ using a theorem of Waldspurger about period integrals for $GL_2$ and
also an extension of the theorem of Saito-Tunnell by this author which was
earlier proved only in odd residue characteristic.}
