diff --git a/Package.swift b/Package.swift
index ad66499..28911e0 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,7 +1,9 @@
-// swift-tools-version:3.1
+// swift-tools-version:4.2
 
 import PackageDescription
 
 let package = Package(
-    name: "NeuralNet"
+	name: "NeuralNet",
+	products: [ .library(name: "NeuralNet", targets: ["NeuralNet"]) ],
+	targets: [ .target(name: "NeuralNet", path: "Sources") ]
 )
diff --git a/Sources/Activation.swift b/Sources/Activation.swift
index e76f024..5fb1ab7 100644
--- a/Sources/Activation.swift
+++ b/Sources/Activation.swift
@@ -302,7 +302,10 @@ public extension NeuralNet {
                     // TODO
                     break
                 case .sigmoid:
-                    result = zip(real, target).map{(-$0 * (1 - $0) * ($1 - $0))}
+					result = zip(real, target).map({ (arg0) -> Float in
+						let (f1, f2) = arg0
+						return (-f1 * (1 - f1) * (f2 - f1))
+					})
                 case .softmax:
                     vDSP_vsub(target, 1,
                               real, 1,
@@ -312,9 +315,6 @@ public extension NeuralNet {
                     gradient(real, target, &result, rows, cols)
                 }
             }
-            
         }
-        
     }
-    
 }