When interfaces between ordered domains are ordered clusters, frustration disappears. A phase with mixed ordered structures emerges but no length scale can be associated to. We show that sum of densities of each structure plays the role of order parameter. For, we consider a regular half full lattice with repulsive interaction extended to second neighboring particles. Ordered structures are p(2X2) when ratio between second and first neighboring interaction energies R=J SN /J FN <0.5 and degenerate p(2X1)/p(1X2) for R>0.5. The ground states coexist with another named p(4X2)/p(2X4) at central bi-critical point: a state to cross when passing between non-frustrated ordered phases.
