Update zero-length detection

difference.go

@@ -15,12 +15,12 @@ func Difference[E Elem[E]](z, x, y Set[E]) Set[E] {
 	inv := false
 
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-			inv = !inv
-		}
+		if len(x) == 0 || len(y) == 0 {
+			if len(x) == 0 {
+				x, y = y, x
+				inv = !inv
+			}
 
-		if len(y) == 0 {
 			if !inv {
 				z = append(z, x...)
 			}

intersection.go

@@ -13,11 +13,7 @@ func Intersection[E Elem[E]](z, x, y Set[E]) Set[E] {
 	z = z[:0]
 
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-		}
-
-		if len(y) == 0 {
+		if len(x) == 0 || len(y) == 0 {
 			return z
 		}
 

issubsetof.go

@@ -7,12 +7,12 @@ func (x Set[E]) IsSubsetOf(y Set[E]) bool {
 	inv := false
 
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-			inv = !inv
-		}
+		if len(x) == 0 || len(y) == 0 {
+			if len(x) == 0 {
+				x, y = y, x
+				inv = !inv
+			}
 
-		if len(y) == 0 {
 			return inv || len(x) == 0
 		}
 

overlap.go

@@ -5,11 +5,7 @@ import "sort"
 // Overlaps reports whether the intersection of x and y is not empty.
 func (x Set[E]) Overlaps(y Set[E]) bool {
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-		}
-
-		if len(y) == 0 {
+		if len(x) == 0 || len(y) == 0 {
 			return false
 		}
 

symdiff.go

@@ -15,13 +15,12 @@ func SymmetricDifference[E Elem[E]](z, x, y Set[E]) Set[E] {
 	z = z[:0]
 
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-		}
+		if len(x) == 0 || len(y) == 0 {
+			if len(x) == 0 {
+				x, y = y, x
+			}
 
-		if len(y) == 0 {
-			z = appendIntervals(z, x...)
-			return z
+			return appendIntervals(z, x...)
 		}
 
 		if x[0].High.Compare(y[0].High) > 0 {

union.go

@@ -13,11 +13,11 @@ func Union[E Elem[E]](z, x, y Set[E]) Set[E] {
 	z = z[:0]
 
 	for {
-		if len(x) == 0 {
-			x, y = y, x
-		}
+		if len(x) == 0 || len(y) == 0 {
+			if len(x) == 0 {
+				x, y = y, x
+			}
 
-		if len(y) == 0 {
 			return append(z, x...)
 		}