Is distinguishing Hadamard matrices _really_ NP-hard? Posted by Alex Meiburg, at cs.stackexchange.com, 10 Oct 2018 In a few different places ( http://www.ams.org/journals/mcom/2004-73-246/S0025-5718-03-01539-4/S0025-5718-03-01539-4.pdf and…