River-Crossing & Constraints
📋 What it is
River-crossing puzzles have RULES about what can be left together; the trick is respecting every constraint each step.
🗣️ Coach says
The classic: a fox, a goose, and grain must cross, but the fox eats the goose and the goose eats the grain if left alone together. The whole puzzle is obeying constraints — you sometimes have to bring something BACK to keep the rules.
🧠 Memory hook
List the “can’t be left together” rules first, then never break one — even if it means going back.
😂 Giggle
Why did the tricky question feel proud?
Because it made everyone stop and think twice!
😲 Whoa!
The fox-goose-grain puzzle appears in a book from around the year 800 CE — over 1,200 years old and still fooling people who forget you sometimes must row BACK.
✅ Quick check: In fox-goose-grain, why might you carry something BACK across the river?
Say your answer out loud first — then reveal.
To avoid leaving a forbidden pair alone — going back is sometimes the only way to keep every constraint satisfied.
Constraint puzzles often need “backward” moves to avoid breaking a rule.
🧪 Try it! (2 minutes)
Solve the fox-goose-grain puzzle by writing the “can’t be alone together” pairs first, then plan crossings.