Add +- operators to AcPower

csharp/Lib/Units/Composite/AcPhase.cs

@@ -42,4 +42,7 @@ public sealed class AcPhase
     };
 
     public static AcPhase Null { get; } = FromVoltageCurrentPhi(0, 0, 0);
+    
+    
+  
 }

csharp/Lib/Units/Composite/AcPower.cs

@@ -86,5 +86,15 @@ public sealed class AcPower
     
     public static AcPower Null { get; } = FromVoltageCurrentPhi(0, 0, 0);
 
+    public static AcPower operator +(AcPower left, AcPower right) => FromActiveReactive
+    (
+        left.Active + right.Active,
+        left.Reactive + right.Reactive
+    );
+
+    public static AcPower operator -(AcPower p) => FromActiveReactive(-p.Active, p.Reactive);
+    
+    
+    
     public override String ToString() => Active.ToString(); // TODO: show all
 }

csharp/Lib/Units/Power/ActivePower.cs

@@ -11,5 +11,8 @@ public sealed class ActivePower : AcPower
      
     public static implicit operator ActivePower(Double d) => new ActivePower(d);
     public static implicit operator Double(ActivePower d) => d.Value;
+    
+    
+    public static ActivePower operator -(ActivePower d) => -d.Value;
 }