Approximate substitutions and the normal ordering problem - H. Cheballah; Gérard Henry Edmond Duchamp; Karol A. Penson (CoRR, 2008)

Some Open Problems in Combinatorial Physics - Gérard Henry Edmond Duchamp; H. Cheballah (CoRR, 2009)

Combinatorial Deformations: Twisting and Perturbations - Gérard Henry Edmond Duchamp; Christophe Tollu; H. Cheballah; Karol A. Penson; Gleb A. Koshevoy (CoRR, 2009)