[en] The neutron flux for each energy group is expanded in the form α(t) [the sum of 1 = o to N the sum of m = o to 1 (21 + 1)Psub(1)sup(m)(costheta)(psisub(glm)(r,t)cos(mphi) + γsub(glm)(r,t)sin(mphi))] where t is the time, r the position vector, theta and phi the axial and azimuthal angles of direction and g the group subscript. By comparing coefficients of Psub(1)sup(m)(costheta)sub(sin(mphi))sup(cos(mphi)) a set of first order differential equations is obtained. Terms with odd 1 are eliminated giving a series of second order equations which are solved for psisub(glm)r,t) and γsub(glm)(r,t) with even 1. Averaging over space and groups with an adjoint flux weighting results in an equation for α(t) and thus the solution is obtained as odd 1 moments are simply related to those with even l. (author)