Problem

Source: IMOC 2017 C2

Tags: combinatorics, geometry, combinatorial geometry, Invariants



On a large chessboard, there are $4$ puddings that form a square with size $1$. A pudding $A$ could jump over a pudding $B$, or equivalently, $A$ moves to the symmetric point with respect to $B$. Is it possible that after finite times of jumping, the puddings form a square with size $2$?