What do A pos and C pos mean?
The # column is the rank of each listed entry for Maarten J. Titulaer — rank 1 means this entry is where Maarten J. Titulaer has the most articles or citations. A pos and C pos show the reciprocal: the position of Maarten J. Titulaer within that entry's own ranked list, by articles and citations respectively. A low value means Maarten J. Titulaer is among the most prominent contributors for that entry.