Erdős Number

It is the number of "hops" needed to connect the author of a paper with the prolific late mathematician Paul Erdős. A mathematician's Erdős number is 1 if they have coauthored a paper with Erdős; it is 2 if they have not coauthored with Erdős, but have coauthored a paper with someone who has coauthored a paper with Erdős; and so on. To learn more about Erdős numbers, check out the Erdős Number Project.

My Erdős number is currently 4:

• Paul Muhly and Mark Tomforde, Adding tails to C*-correspondences, Documenta Math. 9 (2004), 79--106.
  
  
• R.G. Douglas, P. S. Muhly, and Carl Pearcy, Lifting commuting operators, Michigan Math. J. 15 (1968) 385--395.
  
  
• R. G. Douglas, H. S. Shapiro, and A.L. Shields, Cyclic vectors and invariant subspaces for the backward shift operator, Ann. Inst. Fourier 20 (1970), 37--76.
  
  
• P. Erdős, H. S. Shapiro, and A. L. Shields, Large and small subspaces of Hilbert space, Michigan Math. J. 12 (1965), 169--178.