diff --git a/Quicksort/Quicksort.playground/Contents.swift b/Quicksort/Quicksort.playground/Contents.swift
index bbe5d9b7d..1bbf7b967 100644
--- a/Quicksort/Quicksort.playground/Contents.swift
+++ b/Quicksort/Quicksort.playground/Contents.swift
@@ -1,10 +1,5 @@
 //: Playground - noun: a place where people can play
 
-// last checked with Xcode 9.0b4
-#if swift(>=4.0)
-print("Hello, Swift 4!")
-#endif
-
 import Foundation
 
 // *** Simple but inefficient version of quicksort ***
diff --git a/Quicksort/Tests/QuicksortTests.swift b/Quicksort/Tests/QuicksortTests.swift
index 0a8f1a2a8..c8d9a62e6 100644
--- a/Quicksort/Tests/QuicksortTests.swift
+++ b/Quicksort/Tests/QuicksortTests.swift
@@ -1,13 +1,6 @@
 import XCTest
 
 class QuicksortTests: XCTestCase {
-  func testSwift4() {
-    // last checked with Xcode 9.0b4
-    #if swift(>=4.0)
-      print("Hello, Swift 4!")
-    #endif
-  }
-  
   func testQuicksort() {
     checkSortAlgorithm(quicksort)
   }
diff --git a/Quicksort/Tests/SortingTestHelpers.swift b/Quicksort/Tests/SortingTestHelpers.swift
index d699ec1e4..0c47cde4e 100644
--- a/Quicksort/Tests/SortingTestHelpers.swift
+++ b/Quicksort/Tests/SortingTestHelpers.swift
@@ -1,4 +1,3 @@
-import Foundation
 import XCTest
 
 func randomArray(_ size: Int) -> [Int] {
diff --git a/Quicksort/Tests/Tests-Quicksort.xcodeproj/project.pbxproj b/Quicksort/Tests/Tests-Quicksort.xcodeproj/project.pbxproj
index c1b14e727..923195121 100644
--- a/Quicksort/Tests/Tests-Quicksort.xcodeproj/project.pbxproj
+++ b/Quicksort/Tests/Tests-Quicksort.xcodeproj/project.pbxproj
@@ -86,7 +86,7 @@
 			isa = PBXProject;
 			attributes = {
 				LastSwiftUpdateCheck = 0720;
-				LastUpgradeCheck = 0900;
+				LastUpgradeCheck = 1000;
 				ORGANIZATIONNAME = "Swift Algorithm Club";
 				TargetAttributes = {
 					7B2BBC7F1C779D720067B71D = {
@@ -149,12 +149,14 @@
 				CLANG_WARN_BOOL_CONVERSION = YES;
 				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
+				CLANG_WARN_DEPRECATED_OBJC_IMPLEMENTATIONS = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
 				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
 				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_IMPLICIT_RETAIN_SELF = YES;
 				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
 				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
@@ -187,7 +189,7 @@
 				SDKROOT = macosx;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
-				SWIFT_VERSION = 4.0;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Debug;
 		};
@@ -203,12 +205,14 @@
 				CLANG_WARN_BOOL_CONVERSION = YES;
 				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
+				CLANG_WARN_DEPRECATED_OBJC_IMPLEMENTATIONS = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
 				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
 				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_IMPLICIT_RETAIN_SELF = YES;
 				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
 				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
@@ -234,7 +238,7 @@
 				SDKROOT = macosx;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
 				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
-				SWIFT_VERSION = 4.0;
+				SWIFT_VERSION = 4.2;
 			};
 			name = Release;
 		};
diff --git a/Quicksort/Tests/Tests-Quicksort.xcodeproj/xcshareddata/xcschemes/Tests-Quicksort.xcscheme b/Quicksort/Tests/Tests-Quicksort.xcodeproj/xcshareddata/xcschemes/Tests-Quicksort.xcscheme
index 5b67c6f70..ec81527d1 100644
--- a/Quicksort/Tests/Tests-Quicksort.xcodeproj/xcshareddata/xcschemes/Tests-Quicksort.xcscheme
+++ b/Quicksort/Tests/Tests-Quicksort.xcodeproj/xcshareddata/xcschemes/Tests-Quicksort.xcscheme
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "0900"
+   LastUpgradeVersion = "1000"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
@@ -10,7 +10,6 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      language = ""
       shouldUseLaunchSchemeArgsEnv = "YES">
       <Testables>
          <TestableReference
@@ -31,7 +30,6 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      language = ""
       launchStyle = "0"
       useCustomWorkingDirectory = "NO"
       ignoresPersistentStateOnLaunch = "NO"
diff --git a/Slow Sort/README.markdown b/Slow Sort/README.markdown
index f8cc743cc..f7742b6a3 100644
--- a/Slow Sort/README.markdown	
+++ b/Slow Sort/README.markdown	
@@ -17,19 +17,17 @@ We can decompose the problem of sorting n numbers in ascending order into
 Here is an implementation of slow sort in Swift:
 
 ```swift
-public func slowsort(_ i: Int, _ j: Int) {
-    if i>=j {
-        return
-    }
+func slowSort(_ i: Int, _ j: Int, _ numberList: inout [Int]) {
+    guard if i < j else { return }
     let m = (i+j)/2
-    slowsort(i,m)
-    slowsort(m+1,j)
+    slowSort(i, m, &numberList)
+    slowSort(m+1, j, &numberList)
     if numberList[j] < numberList[m] {
         let temp = numberList[j]
         numberList[j] = numberList[m]
         numberList[m] = temp
     }
-    slowsort(i,j-1)
+    slowSort(i, j-1, &numberList)
 }
 ```
 
@@ -47,4 +45,4 @@ public func slowsort(_ i: Int, _ j: Int) {
 
 *Written for Swift Algorithm Club by Lukas Schramm*
 
-(used the Insertion Sort Readme as template)
\ No newline at end of file
+(used the Insertion Sort Readme as template)
diff --git a/Slow Sort/SlowSort.playground/Sources/SlowSort.swift b/Slow Sort/SlowSort.playground/Sources/SlowSort.swift
index 32bb38505..cf09dcc5d 100644
--- a/Slow Sort/SlowSort.playground/Sources/SlowSort.swift	
+++ b/Slow Sort/SlowSort.playground/Sources/SlowSort.swift	
@@ -1,16 +1,15 @@
 import Foundation
 
-public func slowsort(_ i: Int, _ j: Int, _ numberList: inout [Int]) {
-  if i>=j {
-    return
-  }
+public func slowSort(_ i: Int, _ j: Int, _ numberList: inout [Int]) {
+  guard i < j else { return }
+    
   let m = (i+j)/2
-  slowsort(i, m, &numberList)
-  slowsort(m+1, j, &numberList)
+  slowSort(i, m, &numberList)
+  slowSort(m+1, j, &numberList)
   if numberList[j] < numberList[m] {
     let temp = numberList[j]
     numberList[j] = numberList[m]
     numberList[m] = temp
   }
-  slowsort(i, j-1, &numberList)
+  slowSort(i, j-1, &numberList)
 }