Let V 1 be the (2 j 1 + 1) -dimensional vector space spanned by the states | j 1 m 1 ⟩ ⟩ , m 1 ∈ ∈ { − − j 1 , − − j 1 + 1 , … … , j 1 } , and V 2 the (2 j 2 + 1) -dimensional vector space spanned by the states | j 2 m 2 ⟩ ⟩ , m 2 ∈ ∈ { − − j 2 , − − j 2 + 1 , … … , j 2 } .