On 'anti'-eigenvalues for elliptic systems and a question of McKenna and Walter Bernd KawohlGuido Sweers 35B0535J3035B5035P15elliptic systemspositivity of solutionsconditioned Brownian motionplate equationbeam equationmaximum principle Indiana University Mathematics Journal 2002 text pdf 10.1512/iumj.2002.51.2275 10.1512/iumj.2002.51.2275 en Indiana Univ. Math. J. 51 (2002) 1023 - 1040 state-of-the-art mathematics http://iumj.org/access/