  In the literature, the notion of discrepancy is used in several contexts,
even in the theory of graphs. Here, for a graph $G$, $\{-1, 1\}$ labels are
assigned to the edges, and we consider a family $\mathcal{S}_G$ of (spanning)
subgraphs of certain types, among others spanning trees, Hamiltonian cycles. As
usual, we seek for bounds on the sum of the labels that hold for all elements
of $\mathcal{S}_G$, for every labeling.
