  Weyl’s (1927) paper, referred to by Yang above, is entitled  Quantenmechanik und Gruppentheorie (Quantum Mechanics  and Group Theory). In it, Weyl provides an analysis of the  foundations of quantum mechanics and he emphasizes the fundamental  role Lie groups play in that   theory.[105]  Weyl begins the paper by raising two questions: (1) how do I arrive  at the self-adjoint operators, which represent a given quantity of a  physical system whose constitution is known, and (2), what is the  physical interpretation of these operators and which physical  consequences can be derived from them? Weyl suggests that while the  second question has been answered by von Neumann, the first question  has not yet received a satisfactory answer, and Weyl proposes to  provide one with the help of group theory. 