When declaring an abstract method in a base class, it must either be of regular virtual or dynamic virtual type.

program Produce;

  type
    Base = class
      procedure DaliVision; abstract;
      procedure TellyVision; abstract;
    end;

begin
end.

The declaration above is in error because abstract methods must either be virtual or dynamic.

program Solve;

  type
    Base = class
      procedure DaliVision; virtual; abstract;
      procedure TellyVision; dynamic; abstract;
    end;

begin
end.

It is possible to remove this error by either specifying 'virtual' or 'dynamic', whichever is most appropriate for your application.