The converse is also true: if a sequence has an even sum, it is the degree sequence of a multigraph. The construction of such a graph is straightforward: connect vertices with odd degrees in pairs by a matching, and fill out the remaining even degree counts by self-loops. The question of whether a given degree sequence can be realized by a simple graph is more challenging. This problem is also called graph realization problem and can either be solved by the Erdős–Gallai theorem or the Havel–Hakimi algorithm. The problem of finding or estimating the number of graphs with a given degree sequence is a problem from the field of graph enumeration. More generally, the degree sequence of a hypergraph is the non-increasing sequence of its vertex degrees. A sequence is formula_12-graphic if it is the degree sequence of some formula_12-uniform hypergraph. In particular, a formula_14-graphic sequence is graphic. Deciding if a given sequence is formula_12-graphic is doable in polynomial time for formula_16 via the Erdős–Gallai theorem but is NP-complete for all formula_17 (Deza et al., 2018 ).