Проблем със judgе получавам тази грешка

Линк към кода https://github.com/TheBest15/Interfaces-and-Abstraction---Exercise

Compilation result:

Compiled file is missing. Compiler output: Microsoft (R) Build Engine version 15.8.169+g1ccb72aefa for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restoring packages for ...\NUnitLiteConsoleApp.csproj...
  Restoring packages for ...\PersonInfo.csproj...
  Generating MSBuild file ...\PersonInfo.csproj.nuget.g.props.
  Generating MSBuild file ...\PersonInfo.csproj.nuget.g.targets.
  Restore completed in 424.13 ms for ...\PersonInfo.csproj.
  Generating MSBuild file ...\NUnitLiteConsoleApp.csproj.nuget.g.props.
  Generating MSBuild file ...\NUnitLiteConsoleApp.csproj.nuget.g.targets.
  Restore completed in 706.92 ms for ...\NUnitLiteConsoleApp.csproj.
  PersonInfo -> ...\PersonInfo.dll
Test001.cs(33,9): error CS0246: The type or namespace name 'IBirthable' could not be found (are you missing a using directive or an assembly reference?) [...\NUnitLiteConsoleApp.csproj]
Test001.cs(34,9): error CS0246: The type or namespace name 'IIdentifiable' could not be found (are you missing a using directive or an assembly reference?) [...\NUnitLiteConsoleApp.csproj]

Build FAILED.

Test001.cs(33,9): error CS0246: The type or namespace name 'IBirthable' could not be found (are you missing a using directive or an assembly reference?) [...\NUnitLiteConsoleApp.csproj]
Test001.cs(34,9): error CS0246: The type or namespace name 'IIdentifiable' could not be found (are you missing a using directive or an assembly reference?) [...\NUnitLiteConsoleApp.csproj]
    0 Warning(s)
    2 Error(s)

Time Elapsed 00:00:05.60