FCVerbose is an option for numerous functions that allows to specify a local value of $VeryVerbose inside those functions. When set to a positive integer, all the debugging information inside the function will be given according to the value of FCVerbose, while the debugging output of other functions will be still governed by the value of $VeryVerbose. Following values are common
1 - a brief description of the calculational steps including timings
2 - somewhat more debugging information
3 - lots of debugging output, probably useful only for developers
DiracSimplify[GA[\[Mu], \[Nu], \[Rho], \[Mu], \[Nu]], FCVerbose -> 1]\text{DiracSimplify: Entering.}
\text{DiracSimplify: Normal mode.}
\text{DiracSimplify: Extracting Dirac objects.}
\text{DiracSimplify: Done extracting Dirac objects, timing: }0.03636
\text{DiracSimplify: Doing index contractions.}
\text{DiracSimplify: Index contractions done, timing: }0.000453
\text{DiracSimplify: Applying diracSimplifyEval}
\text{DiracSimplify: diracSimplifyEval done, timing: }0.01655
\text{DiracSimplify: Inserting Dirac objects back into products.}
\text{DiracSimplify: Done inserting Dirac objects back into products, timing: }0.000132
\text{DiracSimplify: Applying SpinorChainTrick.}
\text{DiracSimplify: Done applying SpinorChainTrick, timing: }0.001167
\text{DiracSimplify: Creating the final replacement rule.}
\text{DiracSimplify: Final replacement rule done, timing: }0.000119
\text{DiracSimplify: Expanding the result.}
\text{DiracSimplify: Expanding done, timing: }0.000413
\text{DiracSimplify: Leaving.}
\text{DiracSimplify: Total timing: }0.06579
4 \bar{\gamma }^{\rho }
DiracSimplify[GA[\[Mu], \[Nu], \[Rho], \[Mu], \[Nu]], FCVerbose -> 2]\text{DiracSimplify: Entering.}
\text{DiracSimplify: Normal mode.}
\text{DiracSimplify: Extracting Dirac objects.}
\text{DiracSimplify: Done extracting Dirac objects, timing: }0.008883
\text{DiracSimplify: Doing index contractions.}
\text{DiracSimplify: Index contractions done, timing: }0.000426
\text{DiracSimplify: Applying diracSimplifyEval}
\text{DiracSimplify: diracSimplifyEval: Entering}
\text{DiracSimplify: diracSimplifyEval: Applying DiracTrick.}
\text{DiracSimplify: diracSimplifyEval: DiracTrick done, timing: }0.003183
\text{DiracSimplify: diracSimplifyEval: Applying Dotsimplify.}
\text{DiracSimplify: diracSimplifyEval: Dotsimplify done, timing: }0.002288
\text{DiracSimplify: diracSimplifyEval: Applying DiracTrick.}
\text{DiracSimplify: diracSimplifyEval: DiracTrick done, timing: }0.006512
\text{DiracSimplify: diracSimplifyEval: Applying Dotsimplify.}
\text{DiracSimplify: diracSimplifyEval: Dotsimplify done, timing: }0.002125
\text{DiracSimplify: diracSimplifyEval done, timing: }0.01820
\text{DiracSimplify: Inserting Dirac objects back into products.}
\text{DiracSimplify: Done inserting Dirac objects back into products, timing: }0.000146
\text{DiracSimplify: Applying SpinorChainTrick.}
\text{DiracSimplify: Done applying SpinorChainTrick, timing: }0.001152
\text{DiracSimplify: Creating the final replacement rule.}
\text{DiracSimplify: Final replacement rule done, timing: }0.000123
\text{DiracSimplify: Expanding the result.}
\text{DiracSimplify: Expanding done, timing: }0.000374
\text{DiracSimplify: Leaving.}
\text{DiracSimplify: Total timing: }0.03523
4 \bar{\gamma }^{\rho }
DiracSimplify[GA[\[Mu], \[Nu], \[Rho], \[Mu], \[Nu]], FCVerbose -> 3]\text{DiracSimplify: Entering.}
\text{DiracSimplify: Entering with }\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }
\text{DiracSimplify: Normal mode.}
\text{DiracSimplify: Extracting Dirac objects.}
\text{DiracSimplify: dsPart: }\;\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHeadAll}\left(\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHead}\left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }\right)\right)
\text{DiracSimplify: freePart: }0
\text{DiracSimplify: Done extracting Dirac objects, timing: }0.009456
\text{DiracSimplify: diracObjects: }\left\{\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHead}\left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }\right)\right\}
\text{DiracSimplify: Doing index contractions.}
\text{DiracSimplify: Index contractions done, timing: }0.000418
\text{DiracSimplify: diracObjectsEval after index contractions: }\left\{\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHead}\left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }\right)\right\}
\text{DiracSimplify: Applying diracSimplifyEval}
\text{DiracSimplify: diracSimplifyEval: Entering}
\text{DiracSimplify: diracSimplifyEval: Entering with: }\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }
\text{DiracSimplify: diracSimplifyEval: Applying DiracTrick.}
\text{DiracSimplify: diracSimplifyEval: DiracTrick done, timing: }0.002919
\text{DiracSimplify: diracSimplifyEval: After DiracTrick: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: diracSimplifyEval: Applying Dotsimplify.}
\text{DiracSimplify: diracSimplifyEval: Dotsimplify done, timing: }0.002082
\text{DiracSimplify: diracSimplifyEval: After Dotsimplify: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: diracSimplifyEval: Applying DiracTrick.}
\text{DiracSimplify: diracSimplifyEval: DiracTrick done, timing: }0.006242
\text{DiracSimplify: diracSimplifyEval: After DiracTrick: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: diracSimplifyEval: Applying Dotsimplify.}
\text{DiracSimplify: diracSimplifyEval: Dotsimplify done, timing: }0.002124
\text{DiracSimplify: diracSimplifyEval: After Dotsimplify: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: diracSimplifyEval: Leaving with: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: After diracSimplifyEval: }\left\{4 \bar{\gamma }^{\rho }\right\}
\text{DiracSimplify: diracSimplifyEval done, timing: }0.02049
\text{DiracSimplify: Inserting Dirac objects back into products.}
\text{DiracSimplify: repRule: }\left\{\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHead}\left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }\right)\to 4 \bar{\gamma }^{\rho }\right\}
\text{DiracSimplify: Done inserting Dirac objects back into products, timing: }0.001005
\text{DiracSimplify: Intermediate result: }\left\{4 \bar{\gamma }^{\rho }\right\}
\text{DiracSimplify: Applying SpinorChainTrick.}
\text{DiracSimplify: Done applying SpinorChainTrick, timing: }0.001158
\text{DiracSimplify: After SpinorChainTrick: }\left\{4 \bar{\gamma }^{\rho }\right\}
\text{DiracSimplify: Creating the final replacement rule.}
\text{DiracSimplify: repRule: }\left\{\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHeadAll}\left(\text{FeynCalc$\grave{ }$DiracSimplify$\grave{ }$Private$\grave{ }$dsHead}\left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }\right)\right)\to 4 \bar{\gamma }^{\rho }\right\}
\text{DiracSimplify: Final replacement rule done, timing: }0.000980
\text{DiracSimplify: Expanding the result.}
\text{DiracSimplify: Expanding done, timing: }0.000399
\text{DiracSimplify: After expanding: }4 \bar{\gamma }^{\rho }
\text{DiracSimplify: Leaving.}
\text{DiracSimplify: Total timing: }0.04359
\text{DiracSimplify: Leaving with }4 \bar{\gamma }^{\rho }
4 \bar{\gamma }^{\rho }