Upper and lower indices
See also
Overview.
Here we list a set of rules that allows to reconstruct the positions
of indices (upstairs or downstairs) appearing in FeynCalc
expressions
- Every expression must satisfy Einsteins’s summation convention, both
for Lorentz and Cartesian indices. Single terms containing more than two
identical Lorentz or Cartesian indices are illegal and will lead to
inconsistent results.
- In a contraction of two Lorentz indices it is understood that one of
them is upstairs and the other is downstairs.
- In a contraction of two Cartesian indices, both indices are
understood to be upper indices.
- A free Lorentz or Cartesian index is always understood to be an
upper index