Eq.(\[Eq:23 for IHseesaw\]) leads to $$\left( {{a_ + } + {t_{13}}{a_1}{e^{ - i{\delta _{CP}}}}} \right){a_ - } + \left( {{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}} \right){b_ - } = 0.
\label{Eq:23-simplerIH}$$ Considering Eqs.(\[Eq:13-simplerIH\])-(\[Eq:23-simplerIH\]), we find the following cases:

1.  ${\frac{{{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}}}{{{a_ + } + {t_{13}}{a_1}{e^{ - i{\delta _{CP}}}}}} =  - \frac{{{a_1}}}{{{b_1}}} =  - \frac{{{a_ + }}}{{{b_ + }}} =  - \frac{{{a_ - }}}{{{b_ - }}}}$ for ${{a_ + } + {t_{13}}{a_1}{e^{ - i{\delta _{CP}}}}}\neq 0$, ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}}}\neq 0$ as well as $a_{1,+,-}\neq 0$ and $b_{1,+,-}\neq 0$: Eq.(\[Eq:23-simplerIH\]) with ${a_ + } = {b_ + }{a_1}/{b_1}$ yields either ${b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0$, which is not allowed by the initial conditions, or ${a_1}{a_ - } + {b_1}{b_ - } = 0$ giving $\left| {{m_1}} \right| = \left| {{m_2}} \right|$ from Eq.(\[Eq:masses for IHseesaw\]), which contradicts the fact that $\left| {{m_1}} \right| < \left| {{m_2}} \right|$. This case cannot provide a solution.

2.  ${{a_ + } + {t_{13}}{a_1}{e^{ - i{\delta _{CP}}}} = 0}$: It is readily found that ${{b_ + } + {t_{13}}{b_1}{e^{ - i{\delta _{CP}}}} = 0}$ is the solution. We obtain 