Authors 
														   Tobias H. Colding
							     							   
							   Courant Institute of Mathematical Sciences, New York University, New York, NY  10012, United States   and Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, United States							   							   
							   
														   William P. Minicozzi II
							     							   
							   Department of Mathematics, Johns Hopkins University, Baltimore, MD 21218, United States