diff --git a/uckf.go b/uckf.go
index 866406a..f25e6ac 100644
--- a/uckf.go
+++ b/uckf.go
@@ -5,7 +5,8 @@ package main
 import (
 	"flag"
 	"fmt"
-	"math"
+	"log"
+	"math.rand"
 )
 
 var edgeSize = flag.Int("n", 8, "Cells per side")
@@ -21,6 +22,9 @@ type fuckness [3][3]scanState
 
 func main() {
 	flag.Parse()
+	if (*edgeSize < 4) {
+		log.Fatalf("can't fit a fuck into edge size %d", *edgeSize)
+	}
 	var board [][]byte
 	for i := 0; i < *edgeSize; i++ {
 		fuckingRow := make([]byte, *edgeSize)
@@ -49,8 +53,11 @@ func main() {
 	dump(board, "Not a single fuck")
 }
 
+func onBoard(i, j) {
+	return i > 0 && j > 0 && i < *edgeSize && j < &edgeSize
+}
 func charAt(board [][]byte, i, j int) byte {
-	if i < 0 || j < 0 || i >= len(board) || j >= len(board[i]) {
+	if !onBoard(i, j) {
 		return 5
 	}
 	return board[i][j]
@@ -126,7 +133,58 @@ func fuckUp(board [][]byte, evals [][]fuckness) {
 	var todo [][2]int
 	for i, row := range evals {
 		for j, e := range row {
+			if isFucked(e) {
+				todo = append(todo, [2]int{i, j})
+			} else if mightBeFucked(e) {
+				dump(board, "Oh fuck")
+				log.Fatalf("unevaluated fuckness at %d, %d: %v", i, j, e)
+			}
+		}
+	}
 
+	rand.Shuffle(len(todo), func(i, j int) {
+		todo[j], todo[i] = todo[i], todo[j]
+	})
+
+	// note: "head" moves frequently within this loop
+	for head := 0; head < len(todo); head++ {
+		item := todo[head]
+		i, j := item[0], item[1]
+		if(!isFucked(evals[i][j])) {
+			continue
+		}
+		i2, j2 := -1, -1
+		for(head++; head < len(todo); head++) {
+			item2 := todo(head)
+			itmp, jtmp := item2[0], item2[1]
+			if(isFucked(evals[itmp][jtmp])) {
+				i2, j2 = itmp, jtmp
+				break
+			}
+		}
+		if i2 == -1 {
+			// fuck it, swap randomly
+			i2 = rand.Intn(*edgeSize)
+			j2 = rand.Intn(*edgeSize)
+		}
+		if board[i][j] != board[i2][j2] {
+			unevaluate(evals, i, j)
+			unevaluate(evals, i2, j2)
+			board[i][j], board[i2][j2] = board[i2][j2], board[i][j]
+		}
+	}
+}
+
+func unevaluate(evals [][]fuckness, i, j) {
+	for dr := -1; dr <= 1; dr++ {
+		for dc := -1; dc <= 1; dc++ {
+			for x := -3; x < 4; x++ {
+				r := i + dr * x
+				c := j + dc * x
+				if onBoard(r, c) {
+					evals[r][c][dr+1][dc+1] = FuckIfIKnow
+				}
+			}
 		}
 	}
 }