Equation Icon  ′ Pi = ∂-ℒD2-= ∘------BEy--i--------= sgn(ΠB )y′i, (361 ) ∂Y˙i (1 − E2)|⃗y′|2 + B2 ′2 ′2 Π (σ) = ∂-ℒD2-= ∘------E-|⃗y-|---------= sgn(E )|⃗y-|-, (362 ) ∂E (1 − E2)|⃗y′|2 + B2 |B |