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Tropical Combinatorics

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Minimal Free Resolutions<br />

S = K[x1, . . .,xd] polynomial ring with Z d -grading<br />

deg x a = a<br />

free Z d -graded resolution F• of monomial ideal I ⊆ S is<br />

exact (algebraic) complex of Z d -graded S-modules:<br />

F• : · · · φk+1<br />

−→ Fk<br />

φk<br />

−→ · · · φ2<br />

−→ F1<br />

φ1<br />

−→ F0 → 0<br />

Fi ∼ = <br />

a∈Z d S(−a)βi,a free Z d -graded S-modules<br />

maps φi homogeneous<br />

F0 = S and img φ1 = I<br />

i-th syzygy module img φi+1 ⊂ Fi<br />

resolution minimal if βi,a = dimK Tor S i (I, K)a<br />

fine graded Betti numbers

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