[darcs-users] darcs conflicts/dependencies -- is patch theory the place to start?

[Stephen J. Turnbull]

Ben Franksen writes:

 > The problem is that "observationally equivalent" is easy to judge for a 
 > machine but less so for a human.

I don't think it's easy for either machines or humans, though for
different reasons.  In the particular case of file copies and moves,
though, if the git method of checking for the fraction of unchanged
content doesn't capture the concept of copy/move, I don't know what
does.

 > > That's exactly how it's defined, as the same effect.  However, effect
 > > is difficult to define explicitly, it's like the judge's definition of
 > > pornography: "I know it when I see it."
 > 
 > I am dissatisfied with this kind of statement. There *must* be a precise 
 > meaning of "effect",

Sure.  The problem is that there are lots of them depending on your
primitives, whether you count context as part of the precondition, and
so on.  For a simple example, consider that assuming a particular
version, the effects of a token replace can be perfectly accomplished
by the appropriate combination of hunk patches.  However, if you allow
the version to vary, it cannot.