“…m ∈ p i=1 C i . See, e.g., [Gragnaniello et al, 2012, Pham et al, 2014a,b, Smithyman et al, 2015, Peters and Herrmann, 2017, Esser et al, 2018, Yong et al, 2018, Peters et al, 2018. Alternatively, we can also formulate certain types of inverse problems directly as a feasibility (also known as set-theoretic estimation) or projection problem [Youla and Webb, 1982, Trussell and Civanlar, 1984, Combettes, 1993, 1996.…”