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