The effective interaction between a quark and an anti-quark as obtained previously with by the method of iterated resolvents is replaced by the ↑↓-model and applied to flavor off-diagonal mesons including the π + . The only free parameters are the canonical ones, the coupling constant and the masses of the quarks.The light-cone approach [1] to the bound-state problem in gauge theory [2] aims at solving H LC |Ψ = M 2 |Ψ . If one disregards possible zero modes [4] and works in the light-cone gauge, the (light-cone) Hamiltonian H LC is given as a Fock-space operator in [2], or in the compendium [3]. Its eigenvalues are the invariant mass-squares M 2 of physical particles associated with the eigenstates |Ψ . In general, they are superpositions of all possible Fock states with its many-particle configurations. For a meson, for example, holds [6], attacks this problem by DLCQ. Alternatively, one addresses to reduce the many-body problem behind a field theory to an effective one-body problem. The derivation of the effective interaction becomes then the key issue. By definition, an effective Hamiltonian acts only in the lowest sector of the theory (here: in the Fock space of one quark and one anti-quark) and has the same