The term ‘Chisholm’s Paradox’ has been credited to Graeme Forbes in his “Two Solutions to Chisholm’s Paradox” (1984) The topic has been discussed extensively; see, for example, Salmon 1996. In his discussion of the mereological version of the puzzle, Chisholm mentions Chandler 1966. Lewis 1986 is essential reading here. A good discussion of the whole problem of transworld identity can be found in Mackie 2008.