Add session exercise 4

Exercices/Exercice4/Package.resolved

+{
+  "object": {
+    "pins": [
+      {
+        "package": "LogicKit",
+        "repositoryURL": "https://github.com/kyouko-taiga/LogicKit",
+        "state": {
+          "branch": "master",
+          "revision": "8f2589cacf6a7a0d58cbabb9f178bc4909ca0ac4",
+          "version": null
+        }
+      }
+    ]
+  },
+  "version": 1
+}

Exercices/Exercice4/Package.swift

+// swift-tools-version:4.2
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "Exercice4",
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        .package(url: "https://github.com/kyouko-taiga/LogicKit", .branch("master")),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
+        .target(
+            name: "Exercice4",
+            dependencies: ["LogicKit"]),
+        .testTarget(
+            name: "Exercice4Tests",
+            dependencies: ["Exercice4"]),
+    ]
+)

Exercices/Exercice4/README.md

+# Exercice4
+
+A description of this package.

Exercices/Exercice4/Sources/Exercice4/main.swift

+import LogicKit
+import LogicKitBuiltins
+
+let x: Term = .var("x")
+let y: Term = .var("y")
+let z: Term = .var("z")
+
+let first:  Term  = .var("first")
+let last :  Term  = .var("last")
+let head :  Term  = .var("head")
+let tail :  Term  = .var("tail")
+
+let h1: Term = .var("h1")
+let t1: Term = .var("t1")
+let h2: Term = .var("h2")
+let t2: Term = .var("t2")
+
+let res: Term = .var("res")
+
+var kb: KnowledgeBase = [
+  
+  // Complete the knowledge base !
+  // ...
+  
+]
+
+kb = kb + KnowledgeBase(knowledge: (Nat.axioms + List.axioms))
+
+// Write test below to test your rules !
+
+//let req = kb.ask(.fact("op", x, ...))
+//for binding in req{
+//  print(" Ma fact: ", binding["res"]!)
+//}

Exercices/Exercice4/Tests/Exercice4Tests/Exercice4Tests.swift

+import XCTest
+import class Foundation.Bundle
+
+final class Exercice4Tests: XCTestCase {
+    func testExample() throws {
+        // This is an example of a functional test case.
+        // Use XCTAssert and related functions to verify your tests produce the correct
+        // results.
+
+        // Some of the APIs that we use below are available in macOS 10.13 and above.
+        guard #available(macOS 10.13, *) else {
+            return
+        }
+
+        let fooBinary = productsDirectory.appendingPathComponent("Exercice4")
+
+        let process = Process()
+        process.executableURL = fooBinary
+
+        let pipe = Pipe()
+        process.standardOutput = pipe
+
+        try process.run()
+        process.waitUntilExit()
+
+        let data = pipe.fileHandleForReading.readDataToEndOfFile()
+        let output = String(data: data, encoding: .utf8)
+
+        XCTAssertEqual(output, "Hello, world!\n")
+    }
+
+    /// Returns path to the built products directory.
+    var productsDirectory: URL {
+      #if os(macOS)
+        for bundle in Bundle.allBundles where bundle.bundlePath.hasSuffix(".xctest") {
+            return bundle.bundleURL.deletingLastPathComponent()
+        }
+        fatalError("couldn't find the products directory")
+      #else
+        return Bundle.main.bundleURL
+      #endif
+    }
+
+    static var allTests = [
+        ("testExample", testExample),
+    ]
+}

Exercices/Exercice4/Tests/Exercice4Tests/XCTestManifests.swift

+import XCTest
+
+#if !os(macOS)
+public func allTests() -> [XCTestCaseEntry] {
+    return [
+        testCase(Exercice4Tests.allTests),
+    ]
+}
+#endif
\ No newline at end of file

Exercices/Exercice4/Tests/LinuxMain.swift

+import XCTest
+
+import Exercice4Tests
+
+var tests = [XCTestCaseEntry]()
+tests += Exercice4Tests.allTests()
+XCTMain(tests)
\ No newline at end of file