Gamma matrices with holomorphic indices? Exercise 9.5 (String Theory and M-Theory by Becker Becker Schwartz)

In Exercise 9.5 of String theory text by Becker, Becker and Schwartz, the holomorphic indices are used where
$gamma_7 =
(1-gamma_1)(1-gamma_{bar 1})
(1-gamma_2)(1-gamma_{bar 2})
(1-gamma_3)(1-gamma_{bar 3})$.

The above $gamma_7$ is chirality matrix usually defined by
$gamma_7 = igamma_1gamma_2gamma_3gamma_4gamma_5gamma_6$.

I don’t understand what are $gamma_{bar i}$ matrices with bar indices and relation between the usual indices and holomorphic indices.