diff --git a/src/datetime/dateInterval.ts b/src/datetime/dateInterval.ts
index 02456d1b..2e9da23b 100644
--- a/src/datetime/dateInterval.ts
+++ b/src/datetime/dateInterval.ts
@@ -1,4 +1,5 @@
-import type { Inclusiveness, LocalDateInput, LocalDateUnit } from './localDate'
+import { Inclusiveness } from '../types'
+import type { LocalDateInput, LocalDateUnit } from './localDate'
 import { LocalDate, localDateRange } from './localDate'
 
 export type DateIntervalConfig = DateInterval | DateIntervalString
diff --git a/src/datetime/localDate.ts b/src/datetime/localDate.ts
index 913617a1..e18d84e1 100644
--- a/src/datetime/localDate.ts
+++ b/src/datetime/localDate.ts
@@ -1,6 +1,7 @@
 import { _assert } from '../error/assert'
 import { Iterable2 } from '../iter/iterable2'
 import type {
+  Inclusiveness,
   IsoDateString,
   IsoDateTimeString,
   MonthId,
@@ -12,7 +13,6 @@ import { LocalTime } from './localTime'
 
 export type LocalDateUnit = LocalDateUnitStrict | 'week'
 export type LocalDateUnitStrict = 'year' | 'month' | 'day'
-export type Inclusiveness = '()' | '[]' | '[)' | '(]'
 
 const MDAYS = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
 const DATE_REGEX = /^(\d\d\d\d)-(\d\d)-(\d\d)$/
diff --git a/src/datetime/localTime.ts b/src/datetime/localTime.ts
index 219b51c3..03e53d50 100644
--- a/src/datetime/localTime.ts
+++ b/src/datetime/localTime.ts
@@ -1,6 +1,7 @@
 import { _assert } from '../error/assert'
 import { _ms } from '../time/time.util'
 import type {
+  Inclusiveness,
   IsoDateString,
   IsoDateTimeString,
   MonthId,
@@ -8,7 +9,6 @@ import type {
   UnixTimestampMillisNumber,
   UnixTimestampNumber,
 } from '../types'
-import type { Inclusiveness } from './localDate'
 import { LocalDate } from './localDate'
 
 export type LocalTimeUnit = 'year' | 'month' | 'week' | 'day' | 'hour' | 'minute' | 'second'
diff --git a/src/datetime/timeInterval.ts b/src/datetime/timeInterval.ts
index d8738ba2..983a58a2 100644
--- a/src/datetime/timeInterval.ts
+++ b/src/datetime/timeInterval.ts
@@ -1,5 +1,4 @@
-import type { UnixTimestampNumber } from '../types'
-import type { Inclusiveness } from './localDate'
+import type { UnixTimestampNumber, Inclusiveness } from '../types'
 import type { LocalTimeInput } from './localTime'
 import { LocalTime } from './localTime'
 
diff --git a/src/number/number.util.test.ts b/src/number/number.util.test.ts
index 0cc50b5b..87302439 100644
--- a/src/number/number.util.test.ts
+++ b/src/number/number.util.test.ts
@@ -1,4 +1,4 @@
-import { _inRange, _randomInt, _range, _runLessOften, _sortNumbers } from '../index'
+import { _isBetween, _randomInt, _range, _runLessOften, _sortNumbers } from '../index'
 import { _clamp, _randomArrayItem, _round, _toFixed, _toPrecision } from './number.util'
 
 test('_randomInt', () => {
@@ -27,8 +27,18 @@ test.each([
   [2, 2, 1, false],
   [2, 2, 2, false],
   [2, Number.NEGATIVE_INFINITY, 3, true],
-])('_inRange(%s, %s, %s) === %s', (n, minIncl, maxExcl, result) => {
-  expect(_inRange(n, minIncl, maxExcl)).toBe(result)
+])('_isBetween(%s, %s, %s) === %s', (n, min, max, result) => {
+  expect(_isBetween(n, min, max)).toBe(result)
+})
+
+test.each([
+  [2, 1, 3, true],
+  [2, 2, 3, true],
+  [2, 2, 1, false],
+  [2, 2, 2, true],
+  [2, Number.NEGATIVE_INFINITY, 3, true],
+])('_isBetween(%s, %s, %s) [] === %s', (n, min, max, result) => {
+  expect(_isBetween(n, min, max, '[]')).toBe(result)
 })
 
 test.each([
diff --git a/src/number/number.util.ts b/src/number/number.util.ts
index 578e9005..0c30280f 100644
--- a/src/number/number.util.ts
+++ b/src/number/number.util.ts
@@ -1,4 +1,4 @@
-import { SortDirection } from '../types'
+import type { Inclusiveness, SortDirection } from '../types'
 
 export function _randomInt(minIncl: number, maxIncl: number): number {
   return Math.floor(Math.random() * (maxIncl - minIncl + 1) + minIncl)
@@ -29,14 +29,27 @@ export function _runLessOften(percent: number): boolean {
 // todo: _.random to support floats
 
 /**
- *  _inRange(-10, 1, 5) // false
- * _inRange(1, 1, 5) // true
- * _inRange(3, 1, 5) // true
- * _inRange(5, 1, 5) // false
- * _inRange(7, 1, 5) // false
+ *  _isBetween(-10, 1, 5) // false
+ * _isBetween(1, 1, 5) // true
+ * _isBetween(3, 1, 5) // true
+ * _isBetween(5, 1, 5) // false
+ * _isBetween(7, 1, 5) // false
  */
-export function _inRange(x: number, minIncl: number, maxExcl: number): boolean {
-  return x >= minIncl && x < maxExcl
+export function _isBetween(
+  x: number,
+  min: number,
+  max: number,
+  incl: Inclusiveness = '[)',
+): boolean {
+  if (incl === '[)') {
+    return x >= min && x < max
+  } else if (incl === '[]') {
+    return x >= min && x <= max
+  } else if (incl === '(]') {
+    return x > min && x <= max
+  }
+  // ()
+  return x > min && x < max
 }
 
 export function _clamp(x: number, minIncl: number, maxIncl: number): number {
diff --git a/src/promise/pDelay.test.ts b/src/promise/pDelay.test.ts
index a7f4a1a4..995e9786 100644
--- a/src/promise/pDelay.test.ts
+++ b/src/promise/pDelay.test.ts
@@ -1,11 +1,11 @@
-import { _inRange, pDelayFn, pExpectedError } from '..'
+import { _isBetween, pDelayFn, pExpectedError } from '..'
 import { timeSpan } from '../test/test.util'
 import { pDelay } from './pDelay'
 
 test('pDelay', async () => {
   const end = timeSpan()
   await pDelay(100)
-  expect(_inRange(end(), 90, 160)).toBe(true)
+  expect(_isBetween(end(), 90, 160)).toBe(true)
 })
 
 test('pDelay with return value', async () => {
diff --git a/src/promise/pMap.test.ts b/src/promise/pMap.test.ts
index 43b71c1b..0847c880 100644
--- a/src/promise/pMap.test.ts
+++ b/src/promise/pMap.test.ts
@@ -1,5 +1,5 @@
 import type { AsyncMapper } from '..'
-import { _inRange, _randomInt, _range, AppError, END, ErrorMode, pExpectedError, SKIP } from '..'
+import { _isBetween, _randomInt, _range, AppError, END, ErrorMode, pExpectedError, SKIP } from '..'
 import { timeSpan } from '../test/test.util'
 import { pDelay } from './pDelay'
 import { pMap } from './pMap'
@@ -37,13 +37,13 @@ const mapper: AsyncMapper = async ([val, ms]) => {
 test('main', async () => {
   const end = timeSpan()
   expect(await pMap(input, mapper)).toEqual([10, 20, 30])
-  expect(_inRange(end(), 290, 430)).toBe(true)
+  expect(_isBetween(end(), 290, 430)).toBe(true)
 })
 
 test('concurrency: 1', async () => {
   const end = timeSpan()
   expect(await pMap(input, mapper, { concurrency: 1 })).toEqual([10, 20, 30])
-  expect(_inRange(end(), 590, 760)).toBe(true)
+  expect(_isBetween(end(), 590, 760)).toBe(true)
 })
 
 test('concurrency: 4', async () => {
diff --git a/src/types.ts b/src/types.ts
index ac545957..02bd5690 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -326,3 +326,5 @@ export const _objectAssign = Object.assign as <T extends AnyObject>(
 export type ErrorDataTuple<T = unknown, ERR = Error> = [err: null, data: T] | [err: ERR, data: null]
 
 export type SortDirection = 'asc' | 'desc'
+
+export type Inclusiveness = '()' | '[]' | '[)' | '(]'