Comments on "On blocking zeros in linear multivariable systems" [with reply]

Reference is made to a recently published correspondence by P.G. Ferreira in which concern was expressed about the name 'blocking zeros' given in a paper by R.V. Patel (see ibid., vol.AC-31, p.239-41, Mar. 1986) to a newly defined class of zeros for multivariable linear systems. The commenter refers to a few remarks about some 'well-known' results by Ferreira, and objects to the lack of precision in the wording of two of these remarks. Counterexamples to these 'well-known' results are presented. In replying, the original author claims that Example 1 is not a counterexample to his statement, and objects to some lack of precision in Martin's words.<
>