Beckmann, A., & Buss, S. R. (2005). Separation results for the size of constant-depth propositional proofs. Annals of Pure and Applied Logic, 136(1-2), pp. 30-55. doi:10.1016/j.apal.2005.05.002

Beckmann, Arnold, and Samuel R. Buss. "Separation Results for the Size of Constant-depth Propositional Proofs." Annals of Pure and Applied Logic 136, no. 1-2 (2005): 30-55.

Beckmann, Arnold, and Samuel R. Buss. "Separation Results for the Size of Constant-depth Propositional Proofs." Annals of Pure and Applied Logic 136.1-2 (2005): 30-55.