Cite
HARVARD Citation
Milton, K. (2015) Schwinger's quantum action principle : from Dirac's formulation through Feynman's path integrals, the Schwinger-Keldysh method, quantum field theory, to source theory. [Online]. Cham : Springer. Available from: http://access.bl.uk/ark:/81055/vdc_100073185274.0x000001