The parametrization for L and G takes advantage of the Todorov effective external potential forms (as seen in the above section on the two-body Klein Gordon equations) and at the same time displays the correct static limit form for the Pauli reduction to Schrödinger-like form. The choice for these parameterizations (as with the two-body Klein Gordon equations) is closely tied to classical or quantum field theories for separate scalar and vector interactions. This amounts to working in the Feynman gauge with the simplest relation between space- and timelike parts of the vector interaction. The mass and energy potentials are respectively M i 2 = m i 2 + exp ⁡ ⁡ ( 2 G ) ( 2 m w S + S 2 ) , E i 2 = exp ⁡ ⁡ ( 2 G ( A ) ) ( ε ε i − − A ) 2 , so that exp ⁡ ⁡ L = exp ⁡ ⁡ ( L ( S , A ) ) = M 1 + M 2 m 1 + m 2 , G = exp ⁡ ⁡ G = exp ⁡ ⁡ ( G ( A ) ) = 1 ( 1 − − 2 A / w ) .