On the Lazarev-Lieb extension of the Hobby-Rice theorem

O. Lazarev and E.H. Lieb proved that, given f1,…,fn∈L1([0,1];C), there exists a smooth function Φ that takes values on the unit circle and annihilates span{f1,…,fn}. We give an alternative proof of that fact that also shows the W1,1 norm of Φ can be bounded by 5πn+1. Answering a question raised by Lazarev and Lieb, we show that if p>1 then there is no bound for the W1,p norm of any such multiplier in terms of the norms of f1,…,fn.