where Δ Δ represents any invariant interaction singly or in combination. It has a matrix structure in addition to coordinate dependence. Depending on what that matrix structure is one has either scalar, pseudoscalar, vector, pseudovector, or tensor interactions. The operators S 1 and S 2 are auxiliary constraints satisfying S 1 ψ ψ ≡ ≡ ( S 10 cosh ⁡ ⁡ ( Δ Δ ) + S 20 sinh ⁡ ⁡ ( Δ Δ ) ) ψ ψ = 0 ,