Let S be a smooth algebraic surface in {mathbb {P}}^3({mathbb {C}}). Movasati and Sertöz (Rend. Circ. Mat. Palermo 2:1–17, 2020) associate an ideal I_{alpha (C)} to the primitive cohomology class alpha (C) of C in S. We show that the equations of C can be determined by I_{alpha (C)} under numerical conditions. We apply this result to reconstruct rational curves and arithmetically Cohen-Macaulay curves from their cohomology classes. On the other hand, we show that the class alpha (C) of a rational quartic curve C on a smooth quartic surface S is not even perfect, that is, that I_{alpha (C)} is bigger than the sum of the Jacobian ideal of S and of the homogeneous ideals of curves D in S for which I_{alpha (D)}=I_{alpha (C)}.
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