⁹For current research, see Graser and Stangier (2018); Hofmann et al. (2011); Cassell (2002), and for the related emotions of forgiveness and gratitude, see McCullough and vanOyen-Witvliet (2002) and footnote 18.3.1 in Chapter 16. For practical meditation guidance, see e.g. Salzberg (2002).