public User Transform(UserCreated @event) =>
 new User
 {
     UserName = @event.UserName
 };
 public User Create(UserCreated e) => new User
 {
     UserName = e.UserName
 };
 public void Project(UserCreated @event, IDocumentOperations operations) =>
 operations.Store(new User {
     UserName = @event.UserName
 });