a field-theory motivated approach to computer algebra

## expand_diracbar

Simplify the Dirac bar of a composite object.
Rewrite the Dirac conjugate of a product of spinors and gamma matrices as a product of Dirac and hermitean conjugates. This uses $$\bar\psi = i \psi^\dagger\Gamma^0\,,$$ together with $$\Gamma_m^{\dagger} = \Gamma_0\Gamma_m\Gamma_0 \,.$$ For example,
\bar{#}::DiracBar. \psi::Spinor(dimension=10). \Gamma{#}::GammaMatrix. ex:=\bar{\Gamma^{m n p} \psi};
$$\displaystyle{}\bar{\Gamma^{m n p} \psi}$$
expand_diracbar(_);
$$\displaystyle{}\bar{\psi} \Gamma^{m n p}$$