West is an option for DiracTrace and several other functions that deal with traces of Dirac matrices. The option applies only to the computation of D-dimensional traces with an odd number of \gamma ^5 in the Breitenlohner-Maison-t’Hooft-Veltman (BMHV) scheme. With West -> True (default setting), such traces are computed according to formula (A.5) from Comp. Phys. Comm 77 (1993) 286-298, which is also known as West’s formula. For more details, see the documentation of DiracTrace.