Ch 14.2 The coefficients $\langle j_1, m_1; j_2, m_2 | j, m\rangle$ that relate the uncoupled basis $|j_1, m_1\rangle|j_2, m_2\rangle$ to the coupled basis $|j, m\rangle$ when adding two angular momenta: $|j, m\rangle = \sum_{m_1, m_2}\langle j_1, m_1; j_2, m_2|j, m\rangle|j_1, m_1\rangle|j_2, m_2\r