The main program leads Kara to the tree, calling the method invertLeaf
before each step. This method tests whether Kara is on a leaf; if yes, Kara picks it up, if no, Kara puts one down.
def invertLeaf(kara) if kara.onLeaf kara.removeLeaf else kara.putLeaf end end invertLeaf(kara) while not kara.treeFront kara.move invertLeaf(kara) end