diff --git a/fold.go b/fold.go
index 035796b..717033f 100644
--- a/fold.go
+++ b/fold.go
@@ -4,6 +4,9 @@ func Foldl[T any](xs []T, fx func(T, T) T) T {
 	if len(xs) < 1 {
 		return *new(T)
 	}
+	if len(xs) == 1 {
+		return xs[0]
+	}
 	for i := 1; i < len(xs); i++ {
 		xs[0] = fx(xs[0], xs[i])
 	}
@@ -14,6 +17,9 @@ func Foldr[T any](xs []T, fx func(T, T) T) T {
 	if len(xs) < 1 {
 		return *new(T)
 	}
+	if len(xs) == 1 {
+		return xs[0]
+	}
 	li := len(xs) - 1
 	for i := li - 1; i >= 0; i-- {
 		xs[li] = fx(xs[li], xs[i])
diff --git a/parallel.go b/parallel.go
new file mode 100644
index 0000000..39af049
--- /dev/null
+++ b/parallel.go
@@ -0,0 +1,5 @@
+package lambda
+
+
+
+
diff --git a/parallel/parallel.go b/parallel/parallel.go
new file mode 100644
index 0000000..0aaea52
--- /dev/null
+++ b/parallel/parallel.go
@@ -0,0 +1,56 @@
+package parallel
+
+import (
+	"sync"
+
+	"git.tuxpa.in/a/lambda"
+)
+
+var routineCount int = 1
+
+func SetRoutineCount(n int) {
+	routineCount = n
+}
+
+func Map[T any](xs []T, fx func(T) T) []T {
+	spl := lambda.Split(xs, routineCount)
+	wg := new(sync.WaitGroup)
+	wg.Add(len(spl))
+	for i, v := range spl {
+		go func(ix int, vx []T) {
+			spl[ix] = lambda.Map(vx, fx)
+			wg.Done()
+		}(i, v)
+	}
+	wg.Wait()
+	return lambda.Flatten(spl)
+}
+func Foldl[T any](xs []T, fx func(T, T) T) T {
+	spl := lambda.Split(xs, routineCount)
+	wg := new(sync.WaitGroup)
+	wg.Add(len(spl))
+	tmp := make([]T, len(spl))
+	for i, v := range spl {
+		go func(ix int, vx []T) {
+			tmp[ix] = lambda.Foldl(vx, fx)
+			wg.Done()
+		}(i, v)
+	}
+	wg.Wait()
+	return lambda.Foldl(tmp, fx)
+}
+
+func Foldr[T any](xs []T, fx func(T, T) T) T {
+	spl := lambda.Split(xs, routineCount)
+	wg := new(sync.WaitGroup)
+	wg.Add(len(spl))
+	tmp := make([]T, len(spl))
+	for i, v := range spl {
+		go func(ix int, vx []T) {
+			tmp[ix] = lambda.Foldr(vx, fx)
+			wg.Done()
+		}(i, v)
+	}
+	wg.Wait()
+	return lambda.Foldr(tmp, fx)
+}
diff --git a/transform.go b/transform.go
new file mode 100644
index 0000000..9a5ad10
--- /dev/null
+++ b/transform.go
@@ -0,0 +1,49 @@
+package lambda
+
+func Entries[K comparable, V any](m map[K]V) ([]K, []V) {
+	keys := make([]K, 0, len(m))
+	vals := make([]V, 0, len(m))
+	for k, v := range m {
+		keys = append(keys, k)
+		vals = append(vals, v)
+	}
+	return keys, vals
+}
+
+func Flatten[T any](xss [][]T) []T {
+	return Foldl(xss, Merge[T])
+}
+
+func Merge[T any](a, b []T) []T {
+	return append(a, b...)
+}
+
+//split xs into n groups
+//extra elements will be put in the last array to keep order
+//if len(xs) < n, result will be [][]T{xs}
+func Split[T any](xs []T, n int) [][]T {
+	if n == 0 {
+		return nil
+	}
+	groupSize := len(xs) / n
+	if groupSize == 0 {
+		return [][]T{xs}
+	}
+	idx := 0
+	out := make([][]T, n)
+	for i := 0; i < len(xs); i = i + groupSize {
+		from := i
+		to := i + groupSize
+		if idx == (n - 1) {
+			to = len(xs)
+		}
+		if to >= len(xs) {
+			to = len(xs)
+			out[idx] = append(out[idx], xs[from:to]...)
+			return out
+		}
+		out[idx] = append(out[idx], xs[from:to]...)
+		idx = idx + 1
+	}
+	return out
+}
diff --git a/transform_test.go b/transform_test.go
new file mode 100644
index 0000000..2969898
--- /dev/null
+++ b/transform_test.go
@@ -0,0 +1,70 @@
+package lambda_test
+
+import (
+	"reflect"
+	"testing"
+
+	"git.tuxpa.in/a/lambda"
+)
+
+func TestFlattenIntSix(t *testing.T) {
+	var arr [][]int
+	arr = [][]int{{1}, {2}, {3}, {4}, {6}, {5}}
+	ans := lambda.Flatten(arr)
+	exp := []int{1, 2, 3, 4, 6, 5}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}
+
+func TestSplitIntSix0(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 0)
+	if ans != nil {
+		t.Fatalf("expect %v to be %v", ans, nil)
+	}
+}
+
+func TestSplitIntSix1(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 1)
+	exp := [][]int{{1, 2, 3, 4, 6, 5}}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}
+
+func TestSplitIntSix2(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 2)
+	exp := [][]int{{1, 2, 3}, {4, 6, 5}}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}
+func TestSplitIntSix6(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 6)
+	exp := [][]int{{1}, {2}, {3}, {4}, {6}, {5}}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}
+
+func TestSplitIntSix5(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 5)
+	exp := [][]int{{1}, {2}, {3}, {4}, {6, 5}}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}
+
+func TestSplitIntSix10(t *testing.T) {
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Split(arr, 10)
+	exp := [][]int{{1, 2, 3, 4, 6, 5}}
+	if !reflect.DeepEqual(ans, exp) {
+		t.Fatalf("expect %v to be %v", ans, exp)
+	}
+}