The 1-1 Corner Pattern: Safe Cells Around the Bend

The 1-1-X pattern doesn’t only work along straight walls — it applies around corners too. When two “1"s meet at a wall corner and one’s unrevealed neighbors are a subset of the other’s, the non-overlapping cells are guaranteed safe.

This is one of the most commonly missed patterns by intermediate players. Learning it will immediately improve your ability to solve along the edges of the board.

Also known as: 1-2C, 1-2C+ (corner variant). The “C” denotes the corner application of the 1-2 / 1-1 family of patterns.

How It Works

Picture two “1” cells at a wall corner. The corner “1” has only two unrevealed neighbors (cells A and B). The adjacent “1” around the bend has more unrevealed neighbors, including A and B plus additional cells (C, D, E).

Corner “1”: One mine in {A, B}.
Adjacent “1”: One mine in {A, B, C, D, E}.

Since {A, B} already accounts for one mine and the adjacent “1” only needs one mine total, cells C, D, and E must contain zero mines. They are all safe.

This is subset logic — the corner “1”’s neighbors form a subset of the adjacent “1”’s neighbors, and both require the same mine count.

Why Corners Create Subsets

Corner cells have only 3 neighbors. Edge cells have 5 neighbors. When both are “1"s and they share 2 neighbors, the corner cell’s unrevealed set is automatically a small group contained within the edge cell’s larger set. This geometric arrangement makes subset logic apply naturally.

The corner provides the tight constraint. The adjacent cell uses that constraint to clear its extra neighbors.

Visual Example

W W ? ?
W 1 ? ?
? 1 ? ?
? ? ? ?

The upper-left “1” (corner) has two unrevealed neighbors. The lower “1” shares those same neighbors plus has more below and to the sides. The extra neighbors of the lower “1” are safe.

Recognizing the Pattern Quickly

Scan board corners and wall bends. Any “1” in a corner is a potential trigger.
Check the adjacent number. If the number around the corner is also a “1” (or reduces to a “1” after flag subtraction), the pattern applies.
Identify the overlap. The shared unrevealed cells contain the mine. The extra cells are safe.

The key insight: corner numbers constrain tightly because they have few neighbors. Use those tight constraints to simplify adjacent, less-constrained numbers.

Variations

Different Corner Angles

The pattern works at any wall corner — 90-degree turns on the board perimeter, L-shaped revealed regions in the interior, or any place where the boundary changes direction.

Higher Numbers with Flags

If the corner cell shows “2” with one adjacent flag, it effectively becomes a “1.” If the adjacent cell shows “2” with one adjacent flag, it also becomes a “1.” After reduction, the 1-1 corner pattern applies.

Three Cells Around a Corner

Sometimes the wall wraps such that three “1"s form an L-shape. Apply the subset principle between each adjacent pair to find all safe cells along the bend.

The corner “1” and adjacent “1” share neighbors including diagonals. New players often forget that diagonal cells count. Make sure you correctly identify which unrevealed cells are shared between the two numbers.

1-1-X Pattern — The straight-wall version.
Subset Logic (Safe) — The general principle at work.
Corner Patterns — Other corner-based deductions.
1-3-1 Corner Pattern — Corner variant with mines at the flanks.
2-2-2 Corner Pattern — Saturated corner configurations.
Wall & Edge Patterns — More boundary patterns.
All Minesweeper Patterns — Complete visual guide.