Cartier's simplicity conjecture for the Maass Laplace spectrum

Consider the Laplace spectrum of Maass forms on $SL(2,\mathbb Z)\backslash\mathbb H$. Cartier's simplicity conjecture. The spectrum should be simple: there should not be two linearly independent Maass forms on $SL(2,\mathbb Z)\backslash\mathbb H$ sharing the same eigenvalue. The source lists this among open conjectures supported by numerical evidence.