CHRISTMAS DETAILS

IN THIS YEAR'S Christmas/Millennium Details there are 21 paintings to identify. It takes the form of a kind of advent calendar.

The calendar has 20 windows. Each one shows the detail of a window, taken from a more or less well-known painting - windows open or shut, looking out or looking in.

And, as in an advent calendar, the windows are set in a background picture, which is the 21st painting. It is not a detail but a complete painting - complete, but mostly obscured by the windows set in it.

Please identify all these paintings by title and artist, numbering your answers one to 21. Each painting is by a different painter, and several of them have been used in the competition before. Some of the pictures have variant titles, but as usual anything on the right lines will do.

The sender of the first fully correct entry to be picked from the hat - or failing that, of the entry with the most correct answers - will receive a case of Champagne. Three runners-up will each receive a bottle of Champagne.

Answers, to arrive by Wednesday 5 January, should be sent to CHRISTMAS DETAILS, IoS, 1 Canada Square, Canary Wharf, London E14 5DL. The correct answers and the winners' names will be published on Sunday 16 January. (The solution to Details 463 will be published next week.)