Conjecture on recovering double-point structure from the scheme X2X_2

Let CP2C\subset\mathbb{P}^2 be a rational plane curve with parameterization f{\bf f}, and let X2X_2 be the scheme defined in Section 2. Assume that CC has only double points as singularities, write

Sing(C)={P1,,Pt},\operatorname{Sing}(C)=\{P_1,\dots,P_t\},

and let (X2)1,,(X2)t(X_2)_1,\dots,(X_2)_t be the corresponding subschemes of X2X_2. For each ii, set

Li:=p2p11((X2)i).L_i:=p_2p_1^{-1}((X_2)_i).

The X2X_2 multiple-line conjecture. For every ii, (X2)i(X_2)_i is curvilinear and length(X2)i=δPi\operatorname{length}(X_2)_i=\delta_{P_i}. If PiP_i is an A2mi1A_{2m_i-1} singularity, then LiL_i cuts two curvilinear schemes of length mim_i on CnC_n, whose images under π\pi form a curvilinear subscheme of length mim_i of CC. If PiP_i is an A2miA_{2m_i} singularity, then LiL_i is tangent to CnC_n and cuts a curvilinear scheme of length 2mi2m_i on CnC_n, whose image under π\pi is a curvilinear subscheme of length mim_i of CC.

The conjecture would make it possible to determine the structure and plane coordinates of the double points from X2X_2 and their preimages on P1\mathbb{P}^1; equivalently, an AsA_s singularity should be described by p2p11(X2)Cnp_2p_1^{-1}(X_2)\cap C_n and its projection to CC.

Sources & referencesView supporting material

Primary source

Alessandra Bernardi, Alessandro Gimigliano and Monica Idà, “Singularities of plane rational curves via projections”, arXiv:1609.01877 (2017).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.