diff --git a/CONTRACT.md b/CONTRACT.md
index 5b01d97..7b1f973 100644
--- a/CONTRACT.md
+++ b/CONTRACT.md
@@ -38,21 +38,21 @@ Complete **ONLY** the [Classic](https://github.com/GuildCrafts/core-algorithms/b
 - [x] Tests for `fibonacci()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
 - [x] `collatzConjecture()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
 - [x] Tests for `collatzConjecture()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
-- [ ] `setUnion()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `setUnion()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
-- [ ] `setIntersection()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `setIntersection()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
-- [ ] `setComplement()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `setComplement()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
-- [ ] `setSymmetricDifference()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
-- [ ] Tests for `setSymmetricDifference()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `setUnion()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `setUnion()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `setIntersection()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `setIntersection()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `setComplement()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `setComplement()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
+- [x] `setSymmetricDifference()` algorithm is implemented according to the description in [algorithms.md][algorithms-list].
+- [x] Tests for `setSymmetricDifference()` exist with at least 2 unit tests using valid inputs, and at least 1 unit test using invalid inputs.
 - [ ] Repository includes a README file with basic installation and setup instructions.
-- [ ] All dependencies are properly declared in `package.json`.
-- [ ] All major features are added via pull requests with a clear description and concise commit messages.
+- [x] All dependencies are properly declared in `package.json`.
+- [x] All major features are added via pull requests with a clear description and concise commit messages.
 - [ ] Code uses a linter and there are no linting errors.
-- [ ] Variables, functions, files, etc. have appropriate and meaningful names.
+- [x] Variables, functions, files, etc. have appropriate and meaningful names.
 - [ ] Functions are small and serve a single purpose.
-- [ ] The artifact produced is properly licensed, preferably with the [MIT license][mit-license].
+- [x] The artifact produced is properly licensed, preferably with the [MIT license][mit-license].
 
 ### Stretch
 
diff --git a/src/factorial.js b/src/factorial.js
index cb8372f..3b13a65 100644
--- a/src/factorial.js
+++ b/src/factorial.js
@@ -6,11 +6,19 @@
 // // => 120
 
 export default function factorial(num) {
-  var factorialElements = [num]
-  for (var i = num; i > 1; i--) {
-  factorialElements.push(i - 1)
+    var accumulator = num
+    for (var i = num; i > 1; i--) {
+    accumulator = accumulator * (i - 1)
+    }
+    return accumulator
   }
-  return factorialElements.reduce(function(a,b){
-  return a*b
-  }, 1)
-}
+
+//Other way:
+//   var factorialElements = [num]
+//   for (var i = num; i > 1; i--) {
+//   factorialElements.push(i - 1)
+//   }
+//   return factorialElements.reduce(function(a,b){
+//   return a*b
+//   }, 1)
+// }
diff --git a/src/setComplement.js b/src/setComplement.js
new file mode 100644
index 0000000..208675c
--- /dev/null
+++ b/src/setComplement.js
@@ -0,0 +1,22 @@
+// setComplement
+//
+// Return the complement of two sets.
+//
+// const a = [1, 2, 3, 4]
+// const b = [2, 4, 6, 8]
+// setComplement(a, b)
+// // => [6, 8]
+
+
+export default function setComplement(setA, setB) {
+  if ( !Array.isArray(setA) || !Array.isArray(setB) ) {
+    throw new Error('Invalid input format. Expected two arrays')
+  }
+  let complementArray = []
+  for(let element of setB) {
+    if(!setA.includes(element)) {
+      complementArray.push(element)
+    }
+  }
+  return complementArray
+ }
diff --git a/src/setIntersection.js b/src/setIntersection.js
new file mode 100644
index 0000000..a5a1118
--- /dev/null
+++ b/src/setIntersection.js
@@ -0,0 +1,23 @@
+// setIntersection
+//
+// Return the intersection of two sets.
+//
+// const a = [1, 2, 3, 4]
+// const b = [2, 4, 6, 8]
+// setIntersection(a, b)
+// // => [2, 4]
+
+
+export default function setIntersection(a, b){
+  if ( !Array.isArray(a) || !Array.isArray(b) ) {
+    throw new Error('Invalid input format. Expected two arrays')
+  }
+  let concatArr = a.concat(b)
+  let sortedArr = concatArr.sort()
+
+  function isDuplicate(value, index, array){
+    return array.indexOf(value) !== index
+  }
+  let filteredArr = sortedArr.filter(isDuplicate)
+  return filteredArr
+}
diff --git a/src/setSymmetricDifference.js b/src/setSymmetricDifference.js
new file mode 100644
index 0000000..945cec0
--- /dev/null
+++ b/src/setSymmetricDifference.js
@@ -0,0 +1,30 @@
+// setSymmetricDifference
+//
+// Return the symmetric difference of two sets.
+//
+// const a = [1, 2, 3, 4]
+// const b = [2, 4, 6, 8]
+// setSymmetricDifference(a, b)
+// // => [1, 3, 6, 8]
+
+
+export default function setSymmetricDifference(setA, setB) {
+  if ( !Array.isArray(setA) || !Array.isArray(setB) ) {
+    throw new Error('Invalid input format. Expected two arrays')
+  }
+  let complementArray = []
+  
+  for(let element of setB) {
+    if(!setA.includes(element)) {
+      complementArray.push(element)
+    }
+  }
+  for(let element of setA){
+    if(!setB.includes(element)) {
+      complementArray.push(element)
+    }
+  }
+  return complementArray.sort()
+  }
+
+//
diff --git a/src/setUnion.js b/src/setUnion.js
new file mode 100644
index 0000000..79f5b94
--- /dev/null
+++ b/src/setUnion.js
@@ -0,0 +1,22 @@
+// setUnion
+//
+// Return the union of two sets.
+//
+// const a = [1, 2, 3, 4]
+// const b = [2, 4, 6, 8]
+// setUnion(a, b)
+// // => [1, 2, 3, 4, 6, 8]
+
+export default function setUnion(a, b){
+  if (!Array.isArray(a) || !Array.isArray(b)){
+    throw new Error('Invalid input format. Expected two arrays')
+  }
+  let concatArr = a.concat(b)
+  let sortedArr = concatArr.sort()
+
+  function isUnique(value, index, array){
+    return array.indexOf(value) === index
+  }
+  let filteredArr = sortedArr.filter(isUnique)
+  return filteredArr
+}
diff --git a/test/setComplement_test.js b/test/setComplement_test.js
new file mode 100644
index 0000000..a8159ec
--- /dev/null
+++ b/test/setComplement_test.js
@@ -0,0 +1,27 @@
+import { expect } from 'chai'
+import setComplement from '../src/setComplement'
+
+describe('setComplement', function(){
+
+  it('should be a function', function() {
+    expect(setComplement).to.be.a('function')
+  })
+
+  it('should show the items from set B that are not present in set A', function() {
+    const setA = ['fluffy', 'cat', 'scratchy']
+    const setB = ['scratchy', 'fluffy', 'dog']
+    expect(setComplement(setA, setB)).to.eql(['dog'])
+  })
+
+  it('should show empty set if no items in B are not in A', function() {
+    const setA = ['fluffy', 'cat', 'scratchy']
+    const setB = ['scratchy', 'fluffy']
+    expect(setComplement(setA, setB)).to.eql([])
+  })
+
+  it('throws an error when given invalid inputs', function() {
+    expect(function() {setComplement({}, false)}).to.throw(
+      'Invalid input format. Expected two arrays'
+    )
+  })
+})
diff --git a/test/setIntersection_test.js b/test/setIntersection_test.js
new file mode 100644
index 0000000..871a6a0
--- /dev/null
+++ b/test/setIntersection_test.js
@@ -0,0 +1,20 @@
+import { expect } from 'chai'
+import setIntersection from '../src/setIntersection'
+
+describe('setIntersection', function(){
+
+  it('should be a function', function() {
+    expect(setIntersection).to.be.a('function')
+  })
+
+  it('returns the intersection of two sets', function () {
+    expect(setIntersection([1, 2, 3, 4],[2, 4, 6, 8])).to.eql([2,4])
+    expect(setIntersection([82,90,1], [1, 2, 90])).to.eql([1,90])
+  })
+
+  it('throws an error when given invalid inputs', function() {
+    expect(function() {setIntersection('string')}).to.throw(
+      'Invalid input format. Expected two arrays'
+    )
+  })
+})
diff --git a/test/setSymmetricDifference_test.js b/test/setSymmetricDifference_test.js
new file mode 100644
index 0000000..11f9554
--- /dev/null
+++ b/test/setSymmetricDifference_test.js
@@ -0,0 +1,20 @@
+import { expect } from 'chai'
+import setSymmetricDifference from '../src/setSymmetricDifference'
+
+
+
+describe('setSymmetricDifference', function() {
+
+  it('should be a function', function() {
+    expect(setSymmetricDifference).to.be.a('function')
+  })
+
+  it('returns the symmetric difference of two sets', function() {
+    expect(setSymmetricDifference([1, 2, 3, 4], [2, 4, 6, 8])).to.eql([1, 3, 6, 8])
+  })
+  
+  it('throws an error when given invalid inputs', function() {
+    expect(function() {setSymmetricDifference('string', [1,2])}).
+    to.throw('Invalid input format. Expected two arrays')
+  })
+})
diff --git a/test/setUnion_test.js b/test/setUnion_test.js
new file mode 100644
index 0000000..154031e
--- /dev/null
+++ b/test/setUnion_test.js
@@ -0,0 +1,20 @@
+import { expect } from 'chai'
+import setUnion from '../src/setUnion'
+
+describe('setUnion', function(){
+
+  it('should be a function', function() {
+    expect(setUnion).to.be.a('function')
+  })
+
+  it('returns the union of two sets', function() {
+    expect(setUnion([1,2,3,4],[2,4,6,8])).to.eql([1, 2, 3, 4, 6, 8])
+    expect(setUnion([2,3,4,4],[1,2,3,4])).to.eql([1,2,3,4])
+  })
+
+  it('throws an error when given invalid inputs', function() {
+    expect(function() {setUnion('string')}).to.throw(
+      'Invalid input format. Expected two arrays'
+    )
+  })
+})