The lattice cohomology of a reduced curve singularity was introduced in [4]. It is a bigraded ℤ[U]-module ?* = ⊕_{q,n} ?^{q}_{2n}, that categorifies the δ-invariant and extracts key geometric information from the semigroup of values.
In the present paper we prove three structure theorems for this new invariant: (a) the weight-grading of the reduced cohomology is – just as in the case of the topological lattice cohomology of normal surface singularities [22] – nonpositive; (b) the graded ℤ[U]-module structure of ?⁰ determines whether or not a given curve is Gorenstein; and finally (c) the lattice cohomology module ?⁰ of any plane curve singularity determines its multiplicity.
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