SignedLogWeight Plus

Let w₁ = (s₁, x₁) and w₂ = (s₂, x₂) be two elements of {-1,1} X [-∞, ∞].

Let z₁ = s₁ e^-x₁ and z₂ = s₂ e^-x₂.

Then w₁ ⊕ w₂ = (sgn(z₁+z₂), -log e^-|z₁+z₂|).

-- MichaelRiley - 19 Oct 2010