Prove that |Λ/e| = |Λ|-|P|

34 Views Asked by At

Let Λ be a finite dimensional basic algebra over an algebraically closed field k. Let P be a finitely generated left Λ module and e an idempotent of Λ such that addP = addΛe. we denote by addP (respectively, addΛe) the category of all direct summands of finite direct sums of copies of P(respectively, Λe). How can I prove that |Λ/e| = |Λ|-|P|, where |X| denotes the number of nonisomorphic indecomposable direct summands of X?