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. **