| 31. | This leads to the definition of the Ext functor and the Tor functor.
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| 32. | This leads to the definition of the Ext functor and the Tor functor.
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| 33. | A cyclic set is a contravariant functor from the cyclic category to sets.
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| 34. | Identity of composition of functors is identity functor.
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| 35. | A particular case of this happens when a continuous functor admits a left adjoint.
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| 36. | More generally, any type of limit is right adjoint to a diagonal functor.
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| 37. | Recall that we could also express a sheaf as a special kind of functor.
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| 38. | The forgetful functor is very simple : it just ignores all of the operations.
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| 39. | Then let F be the free group functor.
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| 40. | Swan's theorem asserts that the functor ? is an equivalence of categories.
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