[8 7. A canadian farmer has a field in which lives a herd of n tibetan yaks. The farmer, having drunk too much raksi1 starts believing that the yaks are gossiping about him. He thus decides to partition the field by adding fences, so every yak will be in its own closed area (no two yaks will be together). The farmer inserts fences one at a time; no two of them can cross, although they may touch, and each fence separates an already enclosed part of the fields into two smaller pieces, both of which contain at least one yak (see the picture, in which the fences were added in the order green, light blue, magenta, light red and yellow) a traditional distilled alcoholic beverage in Nepal and Tibet Prove that no matter how the farmer inserts the fences, he will need to build exactly n - 1 fences (not including those that originally delimited the field)