Penelope Jane Farmer is an English fiction writer well known for children's fantasy novels. Her best-known novel is Charlotte Sometimes (1969), a boarding-school story that features a multiple time slip.
Definitely not a book for just anyone. But if you have an interest in twins, for whatever reason, this is a must-read. I loved it! It's an anthology of literature (all kinds--fiction, poetry, psychological and philosophical essays and articles, brief witticisms, and so on). The sectional introductions by the anthologist, a little-known but fabulous children's author who is a twin herself, are fascinating reads in their own right. Unlike some anthologies, this book is probably best enjoyed and appreciated when read cover-to-cover, but you could certainly enjoy just reading particular selections.
mostly fascinating, especially the sections on literary appropriation of the themes. and now i see twins, doubles, doppelgangers and shadows everywhere.