Corollary 9.1.7.9. Let $\kappa \leq \lambda $ be regular cardinals. If $\lambda $ has exponential cofinality $\geq \kappa $, then $\kappa \trianglelefteq \lambda $.
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Corollary 9.1.7.9. Let $\kappa \leq \lambda $ be regular cardinals. If $\lambda $ has exponential cofinality $\geq \kappa $, then $\kappa \trianglelefteq \lambda $.
Proof. The case $\kappa = \lambda $ is trivial (Example 9.1.7.6), and the case $\kappa < \lambda $ follows from Proposition 9.1.7.8. $\square$