Consider the following code (C# 4.0):

public class Foo : LambdaExpression { }

This throws the following design-time error:

Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller)

There's absolutely no problem with public class Foo : Expression { } but, out of curiosity and for the sake of learning, I've searched in Google System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) and guess what: zero results returned (when was the last time you saw that?). Needless to say, I haven't found any documentation on this method anywhere else.

As I said, one can easily inherit from Expression; on the other hand LambdaExpression, while not marked as sealed (Expression<TDelegate> inherits from it), seems to be designed to prevent inheriting from it. Is this actually the case? Does anyone out there know what this method is about?

EDIT (1): More info based on the first answers - If you try to implement Accept, the editor (C# 2010 Express) automatically gives you the following stub:

    protected override Expression Accept(System.Linq.Expressions.ExpressionVisitor visitor)
    {
        return base.Accept(visitor);
    }

But you still get the same error. If you try to use a parameter of type StackSpiller directly, the compiler throws a different error: System.Linq.Expressions.Compiler.StackSpiller is inaccessible due to its protection level.

EDIT (2): Based on other answers, inheriting from LambdaExpression is not possible so the question as to whether or not it is recommended becomes irrelevant. I wonder if, in cases like this, the error message should be Foo cannot implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) because [reasons go here]; the current error message (as some answers prove) seems to tell me that all I need to do is implement Accept (which I can't do).