A ug 2 00 6 A reconstruction problem related to balance equations - I ∗

A modified k-deck of a graph is obtained by removing k edges in all possible ways and adding k (not necessarily new) edges in all possible ways. Krasikov and Roditty used these decks to give an independent proof of Müller’s result on the edge reconstructibility of graphs. They asked if a k-edge deck could be constructed from its modified k-deck. In this paper, we solve the problem when k = 1. We also offer new proofs of Lovász’s result, one describing the constructed graph explicitly, (thus answering a question of Bondy), and another based on the eigenvalues of Johnson graph.