The Luecke’s class of operators
T on a Hilbert space H for which ∥(T − vI)−1∥ = 1∕d(v,W(T)), v∉CLW(T),
where CLW(T) is the closure of the numerical range W(T) of T, has been
generalized by using the concept of generalized numerical ranges due to C. S. Lin.
Also it has been shown that the notions of generalized Minkowski distance
functionals and generalized numerical ranges arise in a natural way for elements of
the Calkin algebra.