Abstract. It is an open problem, posed in , to determine the minimal k such that an open flexible k-chain can interlock with a flexible 2-chain. It was first established in  that there is an open 16-chain in a trapezoid frame that achieves interlocking. This was subsequently improved in  to establish interlocking between a 2-chain and an open 11-chain. Here we improve that result once more, establishing interlocking between a 2-chain and a 10-chain. We present arguments that indicate that 10 is likely the minimum.
Lu, Bin; O'Rourke, Joseph; and Zhong, Jianyuan K., "A 2-Chain Can Interlock With an Open 10-Chain" (2013). Faculty Publications. Paper 24.