for short. It should be remembered that this expression is just shorthand notation for (γ μ p − m). "One over matrix" is otherwise nonsensical. In position space one has S F ( x − − y ) = ∫ ∫ d 4 p ( 2 π π ) 4 e − − i p ⋅ ⋅ ( x − − y ) γ γ μ μ p μ μ + m p 2 − − m 2 + i ε ε = ( γ γ μ μ ( x − − y ) μ μ | x − − y | 5 + m | x − − y | 3 ) J 1 ( m | x − − y | ) .