that ${{a_ + } + {t_{13}}{a_1}{e^{ - i{\delta _{CP}}}} = 0}$ and ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0}$.

3.  $a_1 = 0$: $\left( {{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}} \right){b_ 1 } = 0$ is required and ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}} = 0$ is the solution because ${b_ 1 } = 0$ gives $\left| {{m_1}} \right| = \left| {{m_2}} \right|$. The remaining conditions from Eqs.(\[Eq:13-simplerIH\])-(\[Eq:23-simplerIH\]) are fulfilled by $a_+=0$. For Eq.(\[Eq:12 for IHseesaw\]), $\sin 2{\theta _{12}}\left( {b_1^2 - c_{13}^2\left( {a_ - ^2 + b_ - ^2} \right)} \right) =  - 2\cos 2{\theta _{12}}{c_{13}}{b_1}{b_ - }$ should be satisfied. We obtain that ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}} = 0$ and $a_1 = a_+=0$.

4.  $a_ + = 0$: Either ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0}$ or $b_+=0$ is the solution. If $b_+=0$, Eq.(\[Eq:23-simplerIH\]) yields ${{a_1}{a_ - } + {b_1}{b_ - } = 0}$, which results in ${\left| {{m_1}} \right| = \left| {{m_2}} \right|}$ from Eq.(\[Eq:masses for IHseesaw\]). For ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0}$, $a_1=0$ is derived. We obtain that ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0}$ 