calculates the one-loop Feynman diagram amplitude (n-point, where n≤4 and the highest tensor rank of the integration momenta (after cancellation of scalar products) may be up to 3; unless OneLoopSimplify is used). The argument q denotes the integration variable, i.e., the loop momentum. OneLoop[name, q, amplitude] has as first argument a name of the amplitude. If the second argument has head FeynAmp then OneLoop[q, FeynAmp[name, k, expr]] and OneLoop[FeynAmp[name, k, expr]] tranform to OneLoop[name, k, expr]. NOTICE: While OneLoop is restricted to 't Hooft Feynman gauge, the function OneLoopSimplify does not have this restriction (but is usually slower). WARNING: If you encounter anomalies: The default setting of West is True, i.e., the way is calculated in D dimensions has changed compared to the old FeynCalc version. Please keep in mind that the issue of schemes is inherintly tricky.