def get_present_edges(G, active_years):
    """
    Returns all edges in graph satisfying
    - citing year withing ing_years range
    - cited year < citing year

    Parameters
    ---------
    G: igraph object

    active_years: range of allowable citing years

    Output
    -------
    list of edge tuples (igraph indices)
    """
    min_year = min(active_years)
    max_year = max(active_years)

    return [(e.source, e.target) for e in G.es
            if (min_year <= G.vs[e.source]['year'] <= max_year) and
               (G.vs[e.target]['year'] < G.vs[e.source]['year'])]