= Extremal Reissner-Nordstrom isotropic coordinates
{c}
{title2=$ds^2=-H^{-2}dt^2+H^2d\mathbf x^2,\quad H=1+M/\rho$}
For $M=|Q|>0$ and the exterior areal radius $r>M$, integrate $d\rho/\rho=dr/(r-M)$ and choose $\rho=r-M$. The <Reissner-Nordstrom metric> becomes the displayed form. Constant-time proper distance to $\rho=0$ diverges, but these exterior coordinates do not cover the horizon; ingoing null coordinates are regular there. Infinite spatial throat length therefore does not establish absence of an <event horizon>.
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