Function py_kopf_kmatrix_a2 

pub fn py_kopf_kmatrix_a2(
    tags: &Bound<'_, PyTuple>,
    couplings: [[PyParameter; 2]; 2],
    channel: PyKopfKMatrixA2Channel,
    mass: PyMass,
    seed: Option<usize>,
) -> PyResult<PyExpression>

Construct the fixed Kopf a2 K-matrix amplitude.