Let ˆ𝔞1=𝔰𝔩2𝕂ˆ[𝜎1] be the [[Affine Lie algebras of sl_2|𝜎1-twisted affine Lie algebra of 𝔰𝔩2𝕂]],
and 𝑉 be the corresponding [[Natural Heisenberg algebras|ℤ+12-natural Heisenberg module]] on 𝔥=𝕂𝛼.
Defining
where the second expression used the Normal ordered product.
Skipping over a lot of detail1,
the representation of ˜𝔥[−1] on 𝑉 extends to precisely two irreducible representations