In the case of a central simple algebra "A" over a field "F", the reduced norm provides a generalisation of the determinant giving a map "K"1("A") → "F"∗ and S"K"1("A") may be defined as the kernel. Wang's theorem states that if "A" has prime degree then S"K"1("A") is trivial, and this may be extended to square-free degree. Wang also showed that S"K"1("A") is trivial for any central simple algebra over a number field, but Platonov has given examples of algebras of degree prime squared for which S"K"1("A") is non-trivial.