A characterization of the columns of a T-indistinguishability operator

Two different ways to characterize the columns of a operators are studied. The first one by giving explicit conditions, and second one by defining a new operator (/spl Lambda//sub E/) that has columns as fixed points. Some relevant properties of two known operators (/spl phi//sub E/ and /spl psi//sub E/) are also reviewed, in order to compare them with /spl Lambda//sub E/.