ScalingStacks

Remark 2.24 . [03NK]

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Remark 2.24.

As in §2.5, in the embedded case, the Fukaya category ℱ(M){\mathbin{\mathscr{F}}}(M) has objects (L,E,b)(L,E,b) for (L,E)(L,E) an embedded Lagrangian brane and bb a bounding cochain, but the derived Fukaya category Dbℱ(M)D^{b}{\mathbin{\mathscr{F}}}(M) has objects twisted complexes, consisting of objects (L1,E1,b1),…,(Ln,En,bn)(L_{1},E_{1},b_{1}),\ldots,(L_{n},E_{n},b_{n}) in ℱ(M){\mathbin{\mathscr{F}}}(M) together with bi​j∈C​F∗​((Li,Ei),(Lj,Ej))b_{ij}\in CF^{*}\bigl((L_{i},E_{i}),(L_{j},E_{j})\bigr) for 1⩽i<j⩽n1\leqslant\penalty i<j\leqslant\penalty n satisfying an equation.

In the immersed case, we can regard such a twisted complex as a single object (L,E,b)(L,E,b) in ℱ(M){\mathbin{\mathscr{F}}}(M), where LL is the disjoint union L1∐⋯∐LnL_{1}\amalg\cdots\amalg L_{n}, considered as a single immersed Lagrangian, E|Li=EiE|_{L_{i}}=E_{i}, and bb is a bounding cochain for (L,E)(L,E) built from b1,…,bnb_{1},\ldots,b_{n} and bi​jb_{ij} for i<ji<j. Thus there is no need to add twisted complexes, and we can suppose all objects of Dbℱ(M)D^{b}{\mathbin{\mathscr{F}}}(M) are of the form (L,E,b)(L,E,b).

The idempotent completion Dπℱ(M)D^{\pi}{\mathbin{\mathscr{F}}}(M) of Dbℱ(M)D^{b}{\mathbin{\mathscr{F}}}(M) as in §2.5 could still include objects which are direct summands of some (L,E,b)(L,E,b), but do not have a good geometric interpretation. However, in §3.1 we will conjecture that in the situation we are interested in, Dbℱ(M)D^{b}{\mathbin{\mathscr{F}}}(M) is already idempotent complete, so that we can take all objects of Dπℱ(M)D^{\pi}{\mathbin{\mathscr{F}}}(M) to be of the form (L,E,b)(L,E,b).

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