Symmetric numerical ranges of four-by-four matrices

Numerical Ranges of Composition Operators with Elliptic Automorphism Symbols

“…Then in 2015, Heydari and Abdollahi [8] showed that Bourdon and Shapiro's conjecture is true at least 'for a large class of finite order elliptic automorphisms'. Recently, Patton and her students verified Bourdon and Shapiro's conjecture when ϕ of order 4 in their paper [4].…”