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\begin{document}
blablabla si et seulement si :
\begin{subequations}
\begin{align}
|\omega_2| < 1 \quad ; \quad |\omega_3| <1 \nonumber \\
|\alpha_i|^2 \leq (1-|\omega_i|^2)(1-|\omega_{i+1}|^2), \; i=1,3 \\
|\alpha_2|^2 < (1-|\omega_2|^2)(1-|\omega_3|^2) \nonumber \\
\begin{multlined}[t]|\beta_i (1-|\omega_{i+1}|^2)+ \alpha_i \alpha_{i+1} \cj{\omega_{i+1}} |^2 \leq \left[(1-|\omega_i|^2)(1-|\omega_{i+1}|^2) - |\alpha_i|^2\right] \times \\ \left[(1-|\omega_{i+1}|^2)(1-|\omega_{i+2}|^2) - |\alpha_{i+1}|^2 \right], \; \; \; \; \; i=1,2 \end{multlined} \\
\begin{multlined}[t]
\left| \gamma [(1-|\omega_2|^2)(1-|\omega_3|^2)-|\alpha_2|^2]+\alpha_1 \beta_2 \cj{\omega_2}(1-|\omega_3|^2) + \alpha_3 \beta_1 \cj{\omega_3}(1-|\omega_2|^2) \right. \\ \left. +\beta_1\beta_2\cj{\alpha_2} + \alpha_1\alpha_2\alpha_3 \cj{\omega_2 \omega_3} \right|^2 (1-|\omega_2|^2)(1-|\omega_3|^2) \\
\leq \left[ \left( (1-|\omega_1|^2)(1-|\omega_2|^2) - |\alpha_1|^2 \right) \left( (1-|\omega_2|^2)(1-|\omega_3|^2) - |\alpha_2|^2 \right) - \left| \alpha_1 \alpha_2 \cj{\omega_2} + \beta_1 (1-|\omega_2|^2) \right|^2 \right] \\
\times \left[ \left( (1-|\omega_2|^2)(1-|\omega_3|^2) - |\alpha_2|^2 \right) \left( (1-|\omega_3|^2)(1-|\omega_4|^2) - |\alpha_3|^2 \right) - \left| \alpha_2 \alpha_3 \cj{\omega_3} + \beta_2 (1-|\omega_3|^2) \right|^2 \right]
\end{multlined}
\end{align}
\end{subequations}
ou
\begin{subequations}
\begin{align}
