diff --git a/src/array.go b/src/array.go
index e8b9697..3df7f2c 100644
--- a/src/array.go
+++ b/src/array.go
@@ -597,6 +597,32 @@ func ArArray(arr []any) ArObject {
 			return false, ArErr{}
 		},
 	}
+	val.obj["__NotContains__"] = builtinFunc{
+		"__NotContains__",
+		func(args ...any) (any, ArErr) {
+			if len(args) != 1 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "missing argument",
+					EXISTS:  true,
+				}
+			}
+			for _, v := range arr {
+				res, err := runOperation(operationType{
+					operation: 9,
+					value1:    v,
+					value2:    args[0],
+				}, stack{}, 0)
+				if err.EXISTS {
+					return nil, err
+				}
+				if anyToBool(res) {
+					return false, ArErr{}
+				}
+			}
+			return true, ArErr{}
+		},
+	}
 	val.obj["__Boolean__"] = builtinFunc{
 		"__Boolean__",
 		func(args ...any) (any, ArErr) {
diff --git a/src/buffer.go b/src/buffer.go
index 47ffab5..bad094e 100644
--- a/src/buffer.go
+++ b/src/buffer.go
@@ -139,7 +139,7 @@ func ArBuffer(buf []byte) ArObject {
 			default:
 				return nil, ArErr{
 					TYPE:    "TypeError",
-					message: "expected string or []byte, got " + typeof(x),
+					message: "expected string or buffer, got " + typeof(x),
 					EXISTS:  true,
 				}
 			}
@@ -190,5 +190,170 @@ func ArBuffer(buf []byte) ArObject {
 			}
 		},
 	}
+	obj.obj["append"] = builtinFunc{
+		"append",
+		func(a ...any) (any, ArErr) {
+			if len(a) != 1 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected 1 argument, got " + fmt.Sprint(len(a)),
+					EXISTS:  true,
+				}
+			}
+			a[0] = ArValidToAny(a[0])
+			switch x := a[0].(type) {
+			case number:
+				if x.Denom().Cmp(one.Denom()) != 0 {
+					return nil, ArErr{
+						TYPE:    "TypeError",
+						message: "Cannot convert non-integer to byte",
+						EXISTS:  true,
+					}
+				}
+				buf = append(buf, byte(x.Num().Int64()))
+			case string:
+				buf = append(buf, []byte(x)...)
+			case []byte:
+				buf = append(buf, x...)
+			case []any:
+				for _, v := range x {
+					switch y := v.(type) {
+					case number:
+						if y.Denom().Cmp(one.Denom()) != 0 {
+							return nil, ArErr{
+								TYPE:    "TypeError",
+								message: "Cannot convert non-integer to byte",
+								EXISTS:  true,
+							}
+						}
+						buf = append(buf, byte(y.Num().Int64()))
+					default:
+						return nil, ArErr{
+							TYPE:    "TypeError",
+							message: "Cannot convert " + typeof(v) + " to byte",
+							EXISTS:  true,
+						}
+					}
+				}
+			default:
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected string, buffer or array, got " + typeof(x),
+					EXISTS:  true,
+				}
+			}
+			obj.obj["__value__"] = buf
+			obj.obj["length"] = newNumber().SetInt64(int64(len(buf)))
+			return obj, ArErr{}
+		},
+	}
+	obj.obj["insert"] = builtinFunc{
+		"insert",
+		func(a ...any) (any, ArErr) {
+			if len(a) != 2 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected 2 arguments, got " + fmt.Sprint(len(a)),
+					EXISTS:  true,
+				}
+			}
+			poss := ArValidToAny(a[0])
+			values := ArValidToAny(a[1])
+			if typeof(poss) != "number" {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected number, got " + typeof(poss),
+					EXISTS:  true,
+				}
+			}
+			pos := poss.(number)
+			if pos.Denom().Cmp(one.Denom()) != 0 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "position must be an integer",
+					EXISTS:  true,
+				}
+			}
+			posNum := pos.Num().Int64()
+			switch x := values.(type) {
+			case number:
+				if x.Denom().Cmp(one.Denom()) != 0 {
+					return nil, ArErr{
+						TYPE:    "TypeError",
+						message: "Cannot convert non-integer to byte",
+						EXISTS:  true,
+					}
+				}
+				buf = append(buf[:posNum], append([]byte{byte(x.Num().Int64())}, buf[posNum:]...)...)
+			case string:
+				buf = append(buf[:posNum], append([]byte(x), buf[posNum:]...)...)
+			case []byte:
+				buf = append(buf[:posNum], append(x, buf[posNum:]...)...)
+			case []any:
+				for _, v := range x {
+					switch y := v.(type) {
+					case number:
+						if y.Denom().Cmp(one.Denom()) != 0 {
+							return nil, ArErr{
+								TYPE:    "TypeError",
+								message: "Cannot convert non-integer to byte",
+								EXISTS:  true,
+							}
+						}
+						buf = append(buf[:posNum], append([]byte{byte(y.Num().Int64())}, buf[posNum:]...)...)
+					default:
+						return nil, ArErr{
+							TYPE:    "TypeError",
+							message: "Cannot convert " + typeof(v) + " to byte",
+							EXISTS:  true,
+						}
+					}
+				}
+			default:
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected string or buffer, got " + typeof(x),
+					EXISTS:  true,
+				}
+			}
+			obj.obj["__value__"] = buf
+			obj.obj["length"] = newNumber().SetInt64(int64(len(buf)))
+			return obj, ArErr{}
+		},
+	}
+	obj.obj["remove"] = builtinFunc{
+		"remove",
+		func(a ...any) (any, ArErr) {
+			if len(a) != 1 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected 1 argument, got " + fmt.Sprint(len(a)),
+					EXISTS:  true,
+				}
+			}
+			poss := ArValidToAny(a[0])
+			if typeof(poss) != "number" {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "expected number, got " + typeof(poss),
+					EXISTS:  true,
+				}
+			}
+			pos := poss.(number)
+			if pos.Denom().Cmp(one.Denom()) != 0 {
+				return nil, ArErr{
+					TYPE:    "TypeError",
+					message: "position must be an integer",
+					EXISTS:  true,
+				}
+			}
+			posNum := pos.Num().Int64()
+			buf = append(buf[:posNum], buf[posNum+1:]...)
+			obj.obj["__value__"] = buf
+			obj.obj["length"] = newNumber().SetInt64(int64(len(buf)))
+			return obj, ArErr{}
+		},
+	}
+
 	return obj
 }
diff --git a/src/string.go b/src/string.go
index 700181f..4864cef 100644
--- a/src/string.go
+++ b/src/string.go
@@ -565,7 +565,7 @@ func ArString(str string) ArObject {
 			if typeof(a[0]) != "string" {
 				a[0] = anyToArgon(a[0], false, false, 3, 0, false, 0)
 			}
-			return strings.Join([]string{str, a[0].(string)}, ""), ArErr{}
+			return str + a[0].(string), ArErr{}
 		}}
 	obj.obj["__PostAdd__"] = builtinFunc{
 		"__PostAdd__",
@@ -577,7 +577,7 @@ func ArString(str string) ArObject {
 			if typeof(a[0]) != "string" {
 				a[0] = anyToArgon(a[0], false, false, 3, 0, false, 0)
 			}
-			return strings.Join([]string{a[0].(string), str}, ""), ArErr{}
+			return a[0].(string) + str, ArErr{}
 		}}
 	obj.obj["__Multiply__"] = builtinFunc{
 		"__Multiply__",
@@ -597,6 +597,18 @@ func ArString(str string) ArObject {
 			}
 			return strings.Repeat(str, int(n.Num().Int64())), ArErr{}
 		}}
+	obj.obj["__NotContains__"] = builtinFunc{
+		"__NotContains__",
+		func(a ...any) (any, ArErr) {
+			if len(a) != 1 {
+				return nil, ArErr{"TypeError", "expected 1 argument, got " + fmt.Sprint(len(a)), 0, "", "", true}
+			}
+			if typeof(a[0]) != "string" {
+				return nil, ArErr{"TypeError", "cannot check if string contains " + typeof(a[0]), 0, "", "", true}
+			}
+			a[0] = ArValidToAny(a[0])
+			return !strings.Contains(str, a[0].(string)), ArErr{}
+		}}
 	obj.obj["__Contains__"] = builtinFunc{
 		"__Contains__",
 		func(a ...any) (any, ArErr) {