The Erdös number of Peter Wakker is 2, as is demonstrated by the following references.
Fishburn, Peter C. & Peter P. Wakker (1995), “The Invention of the Independence Condition for Preferences,” Management Science 41, 1130-1144.
Erdös, Paul & Peter Fishburn (1997), “Distinct Distances in Finite Planar Sets,” Discrete Mathematics 175, 97-132.
Paul Erdös, Peter C. Fishburn, & Zoltán Füredi (1991), “Midpoints of Diagonals of Convex n-GONS,” SIAM Journal on Discrete Mathematics 4, 329-341.
My (Peter Wakker's) number is also 2 in the stricter sense of Erdös numbers of the second kind, where many-author papers count less than two-author papers. Here only 230 people in the world have a better number (1) than I do, compared to the 511 people in the less strict sense of Erdös number of the first kind.
Background on the folklore in mathematics about the Erdös number is here.