Consider a compact quantum group G$G$. Let a, b$a, b$ and c$c$ be irreducible unitary corepresentations and assume that c$c$ is contained in a \otimes b$a \otimes b$. Let U$U$ be the intertwiner from the representation Hilbert space of c$c$ to the one of a \otimes b$a \otimes b$ and assume that U$U$ is a partial isometry. By Schur hisSchur's lemma U$U$ is determined up to a phase factor.
Question: Can we assume that U has real (Clebsch-Gordan) coefficients?
If not, is there a good class of examples for which this is true? Or is it true for free orthogonal/unitary QG's?
Question: Can we assume that $U$ has real (Clebsch-Gordan) coefficients?
If not, is there a good class of examples for which this is true? Or is it true for free orthogonal/unitary QG's?