Knuth, Donald E. (June 1968). "Semantics of context-free languages". Mathematical Systems Theory. 2 (2): 127–145. CiteSeerX 10.1.1.455.1434. doi:10.1007/BF01692511. ISSN 0025-5661. S2CID 5182310. QID 56672530. /wiki/Donald_Knuth ↩