Equation Icon  2 t2 − t1 = r12 + (1 + γ)-μ ln r1-+-r2 +-r12-+-(1-+-γ)μ∕c-+ 𝒪 (c−5), (4.4 ) c c3 r1 + r2 − r12 + (1 + γ)μ∕c2