By: ValentinHirschi <valentin.hirschi@gmail.com>
document the Levi-Civita normalization and contract it with components
Idenso's axial trace rule Tr[g5 g^mu g^nu g^rho g^sigma] = 4 eps^{mu nu rho
sigma}, its three-gamma expansion and its pair rule eps(a..) eps(b..) =
det g(a_i, b_j) fix the four-dimensional Minkowski epsilon to eps^{0123} = -i
for g5 = i g^0 g^1 g^2 g^3 (diag(-1,-1,1,1) in the Weyl basis). Document it on
EPSILON_SYMBOL and add contract_epsilon4, which contracts the tensor with four
covectors given by components (eps^{0123} det(rows)), sharing the Leibniz
determinant of the metric-determinant pair rule.
A test simplifies Tr[g5 a b c d] (slashed) with Idenso and evaluates it with
contract_epsilon4 against -i Tr[e0 e1 e2 e3 a b c d], i.e. g5 written with
slashed unit vectors, independently of a Dirac basis.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>