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A solution (u0,v0) of a differential system: {f(u,v,▽u,▽v,… ) = 0,g(u,v,▽u,▽v,… ) = 0,is called trivial if (u0,v0) = (0,0); it is called semi-trivial if (u0,v0) ≠ (0,0) but one of u0 and v0 is 0.