FCCheckSyntax[exp] attempts to detect mistakes and
inconsistencies in the user input. The function returns the original
expression but will abort the evaluation if it thinks that the input is
incorrect. Notice that false positives are possible and it is not
guaranteed that the input which passes FCCheckSyntax is
indeed fully correct.
FCCheckSyntax is also an option for several FeynCalc
routines. If set to True, those functions will try to check
the syntax of the input expressions to detect possible inconsistencies.
However, on large expressions such checks may cost a lot of performance,
which is why this option is set to False by default.
Typical mistake, using Times instead of Dot
in noncommutative products
FCCheckSyntax[GA[mu]*GA[nu]]
\text{\$Aborted}
Another common mistake, Einstein summation convention is violated
FCCheckSyntax[FV[p, \[Mu]] FV[q, \[Mu]] FV[r, \[Mu]]]
\text{\$Aborted}