13. An Arabic Tale. A Flock of Pigeons

$>\Delta \theta \Pi \mathrm{V} \oplus \theta\mathbf{v} \Pi \square \nabla \square \Lambda$

$\oplus \Lambda \nabla \theta \Pi \oplus \mathbf{V V} \varnothing \odot$

ロจ৫ఠ<>VIVOO flew up to a tall tree.

Some of the pigeons perched on the branches, while others settled under the tree. "Those perched on the branches said to those below: If one of you flew up to us, then you would be three times fewer than all of us together, and if one of us flew down to you, then we would be equal in number." How many pigeons were perched on the branches and how many were under the tree? (Tales from One Thousand and One Nights. Night 458)
13. From the condition of the problem, it is clear that the number of pigeons sitting on the branches is two more than those sitting below. Further, it follows from the condition that after one of the pigeons flew up to the branch, the number of pigeons sitting on the branch became twice as many as those sitting on the ground. In addition, at this point, there were four more of them. Therefore, 7 pigeons are sitting on the tree, and 5 under the tree.