" p d q {\displaystyle p\,dq} " ∈ E x t C k − 1 ( C Λ 1 , C D i f f ( Λ ¯ n , C Λ 1 ⊗ Λ ¯ n − k − 1 ) ) {\displaystyle \in \mathrm {Ext} _{\mathcal {C}}^{k-1}\,({\mathcal {C}}\Lambda ^{1},{\mathcal {C}}\mathrm {Dif{}f} ({\bar {\Lambda }}^{n},{\mathcal {C}}\Lambda ^{1}\otimes {\bar {\Lambda }}^{n-k-1}))}
where k {\displaystyle k} is the number of the lines.
"
is the number of the lines.