A sufficient condition for the stability of the range of a positive operator in a Hilbert space is given. As a consequence, we get a class of additive perturbations which preserve regularity of the critical point of a positive operator 0 in a Krein space.
- Operator range,
- Krein space,
- Definitizable operator,
- Critical point
Available at: http://works.bepress.com/branko_curgus/45/