Reflection below a cardinal
= Reflection below a cardinal
A property $P$ reflects below a cardinal $\kappa$ when $\{\mu<\kappa:P(\mu)\}$ is unbounded in $\kappa$. For an <elementary embedding> with <critical point of an elementary embedding>[critical point] $\kappa$, one often proves this by using $\kappa$ as a witness below $j(\kappa)$ in the target and then invoking elementarity.
= Reflects below a cardinal
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