Zweibein
= Zweibein
{title2=$e^A{}_{\mu}$}
A zweibein is a two-dimensional <orthonormal coframe in spacetime>: its components obey $h_{\mu\nu}=\eta_{AB}e^A{}_{\mu}e^B{}_{\nu}$. It converts worldsheet coordinate indices into local Lorentz-frame indices and defines curved gamma matrices $\gamma^\mu=e_A{}^\mu\gamma^A$. The associated <spin connection> supplies the <covariant derivative> of worldsheet spinors. In flat <conformal gauge> the coframe can be constant.