Thank you for giving place to articles on word problems [1, 2]. I am concerned with word problems very much and would like to say something about them also. First of all, in my opinion, any discussion should include a definition of the subject and in such situations it is better to keep as close as possible to the exact meaning of the words. I suggest that a non-word problem is a problem, which...

1.1. Much is known about the distribution of the roots of algebraic equations in half-planes. (Cf. the corresponding parts in the survey [l] by Marden.) In the case of matrix equations, however, there appears to be only one known general result concerning the location of the eigenvalues of a matrix in the left half-plane. This theorem is generally known as Lyapunov’s theorem: (L,) Let A be an n...