In this work an interference picture occurring as a result of inner-shell ionization df an atom in a substance is examined. We focus our attention onthe interference of photoelectron scattered waves inside the surroundings ofan excited atom. Such interference leads to the interdependence ofamplitudes of the photoelectron waves reflected (or back scattered) bydifferent coordination spheres and thus the surroundings act as an indivisiblesystem. The influence of this interference is analysed here using as anexample, the O A'-shell XANES in the N20 molecule (the case of XANESof a terminal atom in a linear triatomic molecule). To reveal the role of theinterferencial effects inside the diatomic fragment (N,-N2) we obtain anapproximate analytical expression for XANES description. Such a description becomes possible due to (i) the localized orbitals approach, (ii) thevariable phase approach and (iii) the concept of electron-optical propertiesof surroundings. The performed calculations show that for the correct OAT-shell XANES interpretation the interference photoelectron waves insidethe fragment must necessarily be taken into account. It is as well stated thatthe interference effects inside the surroundings explain: (1) the disturbance ofthe linear correlation between ff-resonance position and bond length, (2) thetransformation of the EXAFS-like band to the resonance-like line in thespectrum and (3) the appearance of the extra maximum in the u-channel ofthe photoabsorption cross section.