{\mu,\nu,\rho,\sigma}::Indices(position=free).
{a,b,c,d,i,j,k}::Indices(vector).
x::Coordinate.
\partial{#}::Derivative.
f^{a b c}::AntiSymmetric.
F^{i}_{\mu\nu}::Depends(x).
A^{i}_{\mu}::Depends(x,\partial).
\delta{#}::Accent;
S:= -1/4 \int{ F^{i}_{\mu \nu} F^{i \mu \nu} }{x};
rl:= F^{a}_{\mu \nu} -> \partial_{\mu}{A^{a}_{\nu}} - \partial_{\nu}{A^{a}_{\mu}} + g f^{a b c} A^{b}_{\mu} A^{c}_{\nu};
substitute(S, rl);
After I make the substitution, the dummy indices will appear more than twice in the expression and after the
distribute(_)
It will raise an error that triple index b inside a single factor found.