Dirac published the "[[Principles of Quantum Mechanics]]" in 1930, which introduced the widely used [[delta]] [[function]] and [[bra-ket notation]]. Inspired in part by this book, the physicist [[Richard Feynman]] later proposed a path integral formulation of quantum mechanics in 1948. | Dirac published the "[[Principles of Quantum Mechanics]]" in 1930, which introduced the widely used [[delta]] [[function]] and [[bra-ket notation]]. Inspired in part by this book, the physicist [[Richard Feynman]] later proposed a path integral formulation of quantum mechanics in 1948. |