  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.
