An example of substituability test that is recursive

[John Rose]

On Jan 31, 2019, at 10:52 AM, Brian Goetz <brian.goetz at oracle.com> wrote:
> 
> Let’s not do this to Java, shall we?
> 
>     https://twitter.com/seldo/status/1090931182227861508 <https://twitter.com/seldo/status/1090931182227861508>
> 
>> solution 2: you claim it's too complex and you just let the user deal with it by calling equals() (and provide a way for a user to call the default subs).

That one motivated this:

https://twitter.com/JohnRose00/status/1091046489256644608