“…Techniques developed within infinite-dimensional ISS theory include characterizations of ISS and ISS-like properties in terms of weaker stability concepts [26,23], [9,32], constructions of ISS Lyapunov functions for PDEs with distributed and boundary controls [21,31,4,25,37,42], non-coercive ISS Lyapunov functions [26,8], efficient methods for study of boundary control systems [41,9,10,17,20], etc.…”