One can, on demand, produce quick sketches of islands and bridges to make puzzles like the Bridges of Konigsberg—then either challenge them to solve different sets of bridges, to draw their own for you to solve, or (perhaps for older kids) to figure out how their uncle can tell at a glance which puzzles will be possible.
Or if you play with the rule that you can add or remove one bridge before you start, then it should always be solvable, which might be more impressive than “This one is unsolvable, trust me”
One can, on demand, produce quick sketches of islands and bridges to make puzzles like the Bridges of Konigsberg—then either challenge them to solve different sets of bridges, to draw their own for you to solve, or (perhaps for older kids) to figure out how their uncle can tell at a glance which puzzles will be possible.
Or if you play with the rule that you can add or remove one bridge before you start, then it should always be solvable, which might be more impressive than “This one is unsolvable, trust me”
Good suggestion, and the username checks out.