Add project files.

Helloword_core.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.29613.14
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Helloword_core", "Helloword_core\Helloword_core.csproj", "{7F3E676F-BAEB-4B9A-AB3E-9233000E768C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{7F3E676F-BAEB-4B9A-AB3E-9233000E768C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7F3E676F-BAEB-4B9A-AB3E-9233000E768C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7F3E676F-BAEB-4B9A-AB3E-9233000E768C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7F3E676F-BAEB-4B9A-AB3E-9233000E768C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {682729E0-0E3C-47D8-9D5F-EB4386640B22}
+	EndGlobalSection
+EndGlobal

Helloword_core/Hello.cs

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+using System;
+
+namespace Helloword_core
+{
+    public class Hello : IHello
+    {
+        public Hello()
+        {
+            //throw new Exception();
+        }
+
+        string IHello.SayHello()
+        {
+            return "Hello fromn class";
+        }
+    }
+}

Helloword_core/Helloword_core.csproj

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+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Folder Include="wwwroot\" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.App" />
+    <PackageReference Include="Microsoft.AspNetCore.Razor.Design" Version="2.1.2" PrivateAssets="All" />
+  </ItemGroup>
+
+</Project>

Helloword_core/IHello.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Helloword_core
+{
+   public interface IHello
+    {
+        string SayHello();
+    }
+}
+

Helloword_core/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging;
+
+namespace Helloword_core
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            CreateWebHostBuilder(args).Build().Run();
+        }
+
+        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
+            WebHost.CreateDefaultBuilder(args)
+                .UseStartup<Startup>();
+    }
+}

Helloword_core/Properties/launchSettings.json

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+{
+  "iisSettings": {
+    "windowsAuthentication": false, 
+    "anonymousAuthentication": true, 
+    "iisExpress": {
+      "applicationUrl": "http://localhost:49675",
+      "sslPort": 44324
+    }
+  },
+  "profiles": {
+    "IIS Express": {
+      "commandName": "IISExpress",
+      "launchBrowser": true,
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "Helloword_core": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "applicationUrl": "https://localhost:5001;http://localhost:5000",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

Helloword_core/Startup.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Helloword_core
+{
+    public class Startup
+    {
+        // This method gets called by the runtime. Use this method to add services to the container.
+        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
+        public void ConfigureServices(IServiceCollection services)
+        {
+            services.AddSingleton<IHello, Hello>();
+        }
+
+        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
+        public void Configure(IApplicationBuilder app, IHostingEnvironment env, IHello novo)
+        {
+            if (env.IsDevelopment())
+            {
+                app.UseDeveloperExceptionPage();
+            }
+
+
+
+            app.Run(async (context) =>
+            {
+                await context.Response.WriteAsync(novo.SayHello());
+            });
+        }
+    }
+}