1. Allen, R.G.D., 1959, Mathematical Economics, Chap. 8, Sects. 8.4, 8. 5.
2. Allen, R.G.D., 1967, Macro-Economic Theory: A Mathematical Treatment, Chap. 19, Sects. 19.3, 19. 4.
3. Gellman, R. and K.L. Cooke, 1963, Differential-Difference Equations, Chaps.3, 4, 13.
4. Bergstrom, A.R., 1967, The Construction and Use of Economic Models,pp. 1-2.
5. Bergstrom, A.R. (ed.), 1976, Statistical Inference in Continuous Time Models.