K Orr defined a Milnor-type invariant of links that lies in the third homotopy group of a certain space . The problem of nontriviality of this third homotopy group has been open. We show that it is an infinitely generated group. The question of realization of its elements as links remains open.
"On the third homotopy group of Orr's space." Algebr. Geom. Topol. 18 (1) 569 - 582, 2018. https://doi.org/10.2140/agt.2018.18.569