1. Bateman, P.T., Horn, R.A.: A heuristic asymptotic formula concerning the distribution of prime numbers. Math. Comput.16, 363–367 (1962)
2. Buchstab, A.A.: Combinatorial intensification of the sieve method of Eratosthenes (in Russian). Uspehi Mat. Nauk22, no. 3 (135), 199–226 (1967)
3. Chen, J.-R.: On the distribution of almost-primes in an interval. Sci. Sinica18, 611–627 (1975)
4. Friedlander, J., Iwaniec, H.: Quadratic polynomials and quadratic forms, (to appear in Acta Math.),
5. Halberstam, H., Richert, H.-E.: Almost-primes in short intervals and arithmetic progressions (unpublished),