Hi. Before question, sorry about my bad english. It's not my mother tongue. My QM textbook(Schiff) adopt J x J = i(h bar)J. as the defining equations for the rotation group generators in the general case. My question is, then tensor J must have one index which has three component? (e.g. x-y-z or rho-theta-z or r-theta-pi) And, i also have one question about position operator. In wikipedia, its eigen'value' is said to be particle's position 'vector'. What this mean is that position operator is (rank 3) tensor operator? Thanks for reading.