production in the GPD formalism. We also discuss the generalization of Abel transform to- mography approach for the case of gluons. We argue that the dual parametrization provides opportunities for the more flexible modeling GPDs in a nucleon. We strongly suggest to use the fitting strategies based on the dual parametrization to extract the information on GPDs from the experimental data. Let us also stress that in principle there is no essential difference between the dual parametrization of GPDs and the Mellin-Barnes representation with the expansion of Gegenbauer moments in the in the t -channel SO(3) [12, 14] (see dis- cussion in [45]). However, the full inversion formula relating the two parametrizations is still unknown. I would especially like to thank Maxim Polyakov for valuable help and for discussing this article with me. I am grateful to Dieter M¨ uller for numerous illuminating conversations and for careful reading of the manuscript. I am also thankful to Igor Anikin, Alena Moi- seeva, Bernard Pire, Lech Szymanowski, Mark Vanderhaeghen and Samuel Wallon for many discussions and helpful comments. I also acknowledge much the partial support from P2I. The method suggested in [15] for the summation of the formal partial wave expansions of the type (18) for GPDs in the framework of the dual parametrization consists in presenting GPD as the result of convolution of a certain convolution kernel with the set of forward like functions whose Mellin moment generate the generalized form factors B$_{nl}$ . The explicit form of the corresponding convolution kernel was presented in [15] for the case of quark GPD (see also [22] for the refined version of the derivation). In this appendix we present the summary of relations employed for the derivation of the integral transformation (28) expressing GPDs H g ( E ) through the set of the forward like functions G ( E ) 2 ν . We introduce the common useful variable A. SUMMING UP THE FORMAL SERIES FOR UNPOLARIZED GLUON GPDS Acknowledgements z$_{s}$ = 2 z − ξs (1 s $^{2}$) y , (A1) 28