Step 1: construct an element of
Consider an element of corresponding to the extension:
(Remember that is defined in Eq. (15).)
Step 2: compose it with an intertwiner
There exists a -invariant map
Composing it with the element of we get a class in .
We will now describe this intertwiner.
Construction of the intertwiner of Eq. (19)
Intertwiner: algebraic preliminaries
Suppose that we have an associative algebra . For any consider their product:
In particular, take — the algebra of supermatrices. Let us view the exterior product as a subspace in .
For any element we define:
It defines a map:
Description of the intertwiner
For and belonging to , we define: