The Vertex Algebra M(1)+ and Certain Affine Vertex Algebras of Level-1

We give a coset realization of the vertex operator algebra M(1)(+) with central charge l. We realize M(1)(+) as a commutant of certain affine vertex algebras of level -1 in the vertex algebra L-Cl (1) (-1/2 Lambda(0)) circle times L-Cl (1) (-1/2 Lambda(0)). We show that the simple vertex algebra L-Cl (1) (-1 Lambda(0)) can be (conformally) embedded into LA2l-1(1) (-Lambda(0)) and find the corresponding decomposition. We also study certain coset subalgebras inside L-Cl (1)(Lambda(0)).