Consider a continuous function on a metric space. In the presence of linking between a compact pair and a closed set, depending on the different behaviors of the function on the linking sets, we establish minimax results guaranteeing existence of Palais-Smale sequences or providing gradient estimates. Our approach relies on deformation techniques.
V. V. Motreanu. "Minimax Results with Respect to Different Altitudes in the Situation of Linking." Abstr. Appl. Anal. 2013 (SI61) 1 - 6, 2013. https://doi.org/10.1155/2013/781746