It is common to make use of abstract index notation for the vector fields, in which case the vector fields all come with a Lorentzian index , like so: formula_3, and formula_4. If abstract index notation is used also for spinors then these will carry a spinorial index and the Dirac gamma will carry one Lorentzian and two spinorian indices, but it is more common to regard spinors as column matrices and the Dirac gamma as a matrix which additionally carries a Lorentzian index. The Feynman slash notation can be used to turn a vector field into a linear operator on spinors, like so: formula_5; this may involve raising and lowering indices.