(July 22, 2016, 2:25 PM EDT) -- CHICAGO — An art historian may opine that if a signature were authenticated, the market value for a piece of art would be between $6 million and $8 million, an Illinois federal judge ruled July 21, declining to exclude the historian’s testimony (Robert Fletcher and Bartlow Gallery Ltd. v. Peter Doig, No. 13-3270, N.D. Ill.; 2016 U.S. Dist. LEXIS 95081)....