= Reissner-Nordstrom trapped spheres
{c}
{title2=$r_-<r<r_+$}
In ingoing <Reissner-Nordstrom spacetime>, orient $-\partial_r$ to the future and normalize the other radial <null vector> to $\partial_v+(f/2)\partial_r$. The <spherical null expansion in ingoing coordinates> gives $-2/r$ and $f/r$. Hence the strictly future <trapped surfaces> among the round spheres occur exactly between the distinct horizons. At either horizon the outgoing <null expansion> vanishes. Inside the inner horizon the same round spheres are not future trapped.
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