"Good" (quantum) number and 恩賜之絲竹

"Good" quantum number. We often meet this term on the fundamental textbook of QM or QP. But, when one is who study QM the first time, or, even is the researcher would not have idea for this term.Like as Configuration Interaction, I might say that is the off-diagonal parts. But, 「不協和音」is the best for…