Generators and relations for (generalised) Cartan type superalgebras

In Kac’s classification of finite-dimensional Lie superalgebras, the contragredient ones can be constructed from Dynkin diagrams similar to those of the simple finite-dimensional Lie algebras, but with additional types of nodes. For example, $A(n-1,0)=\mathfrak{s}\mathfrak{l}(1\mathrm{\mid }n)$ can be constructed by adding a “gray” node to the Dynkin diagram of $A_{n-1}=\mathfrak{s}\mathfrak{l}(n)$, corresponding to an odd null root. The Cartan superalgebras constitute a different class, where the simplest example is $W(n)$, the derivation algebra of the Grassmann algebra on $n$ generators. Here we present a novel construction of $W(n)$, from the same Dynkin diagram as $A(n-1,0)$, but with additional generators and relations.