Masyu: pearls near the edge
A pearl with no room on one side has only one way to go. Look for pearls near the edge, and for pearls that crowd each other.
How it works
Every pearl rule needs room. A black pearl sends out two legs, and each leg runs through two squares. A white pearl goes straight through, so it needs a free square on both sides.
So look where room runs out: next to the edge of the grid, and next to other pearls. Each pattern below is a small proof by contradiction. Try the other way, and some pearl can’t keep its rule.
Worth memorizing
Black pearl near an edge: its leg goes the other way.
A leg needs two squares of room.
White pearl on an edge: it runs along the edge.
Three white pearls in a row: the loop crosses the row at each.
Two black pearls side by side: their legs point apart.
Practice
0 of 4 rightWhich way does this black pearl’s up-or-down leg go?
Three white pearls stand in a column. Which ways does the loop leave the middle one?
Which way does the left pearl’s sideways leg go?
Can a white pearl sit in a corner square?