This seasonally themed picture logic puzzle was created by Professor Barry O'Sullivan, Head of Computer Science, University College Cork.
A version of it appeared in last week's Science of Christmas supplement, but some of the clues were incorrect.
It is called a nonogram, in which you fill in certain cells (and leave the others blank) to reveal a picture that has been encoded in them, (in this case a Christmas tree). Example above.
There are 15 squares across and 15 squares down. Clues are given on each row and column.
In a clue with a single figure such as 3, three adjoining squares in the corresponding row or column are filled in.
A clue like 2 3 1 means that the corresponding row or column contains sets of two, three and one filled squares, with at least one blank square between each of these sets.
A hint is to start with clues with very large numbers, the largest being 15.