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368    19. Higher Dimensional Analogs of Elliptic Curves: Calabi–Yau Varieties

                              d         d          d         d
              0 −−−−→ O X −−−−→ &   1  −−−−→ ... −−−−→ & i  −−−−→ ... .
                                    X                    X
                            i, j
        The spectral sequence E r is defined for all r ≥ 1 with differentials
                                     i, j   i+r, j−r+1
                                d r : E r  → E r
        such that H(E r , d r ) = E r+1 .
                                                 p,q    p+1,q
           In dimension 1, we have the differential d 1 : E  → E
                                                1       1
                                                1
                              0
                                                     1
                            H (X, O X ) −−−−→ H (X,& )
                                                     X
                                                     1
                              0
                                                1
                            H (X, O X ) −−−−→ H (X,& )
                                                     X
                                              p,q    p+1,q
        In dimension 2, we have the differential d 1 : E  → E
                                             1       1
                     2
                                                              2
                                      2
                                            1
                                                        2
                   H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& )
                                            X                 X
                                      1
                                                        1
                                                              2
                     1
                                            1
                   H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& )
                                            X                 X
                                            1
                                      0
                                                              2
                     0
                                                        0
                   H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& ).
                                            X                 X
                                              p,q    p+1,q
        In dimension 3, we have the differential d 1 : E  → E
                                             1       1
                                               3
                                                     2
                                                                       3
                                   1
            3
                              3
                                                                 3
           H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& ) −−−−→ H (X,& )
                                    X                X                 X
                                                     2
                                               2
            2
                              2
                                   1
                                                                 2
                                                                       3
           H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& ) −−−−→ H (X,& )
                                    X                X                 X
                                                                       3
                                                     2
                              1
                                                                 1
                                   1
                                               1
            1
           H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& ) −−−−→ H (X,& )
                                    X                X                 X
                                                                 0
                              0
            0
                                                                      3
                                                     2
                                               0
                                   1
           H (X, O X ) −−−−→ H (X,& ) −−−−→ H (X,& ) −−−−→ H (X,& ).
                                    X                X                X
           The differentials d r with r ≥ 1 are all zero for smooth algebraic varieties and
        K¨ ahler manifolds.
        (6.9) Poincar´ e Dualityand Serre Duality. For a complex manifold X of complex
        dimension n we have a nondegenerate pairing
                               H i  (X) × H 2n−i (X) → C
                                DR       DR
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