* If you've found this document from a search engine, you should
  start reading here instead: http://www.danceswithferrets.org/xor/


[George Foot on Ovine's XOR remake:]

                Specifically, they got one thing right - if you move
vertically, the chickens get to move first, otherwise the fish get to
move first.  That's obviously quite important in a lot of the puzzles.
But in the BBC version, *all* the chickens move, then *all* the fish,
etc, whereas in the Ovine version it's possible for a chicken to get
stuck in a line of fish - like this:

    *F       *F
	*FC      *C
	*M   =>  *F
	***      ***

On the BBC version, the chicken would not have moved, and both fish
would have fallen one square each.  I quickly ran into some practical
cases of puzzles needing an extra chicken from somewhere else, or of
puzzles just being easier through this rule change - it's quite
disconcerting when rules you're so used to start being broken!

Other oddities compared to the BBC version include exploding sad masks
not toggling the wall hiding state, and allowing the user to skip to
levels 11/13/15.  On the BBC you can only play level 11 if you've just
completed level 10 - if you die, you're back to level 10 again.
Particularly annoying for level 12, I found, as it's a bit of a
marathon. [But at least one of the original XOR releases - the Spectrum
one - didn't have this limitation, so perhaps Ovine worked from that.]

They also added a mode where the screen is always centred around your
character, as opposed to the "classic" mode where it only scrolls when
you move right to the edge.  It's much easier their way, but I'm torn on
whether the loss of "secrecy" is a good or bad thing - I'm not generally
keen on being expected to solve problems without having all the facts
presented to me!

Then again, I work in software development, so there is that expectation
a lot of the time.


Playing through the Ovine version so soon after completing the BBC
version highlighted the problem with their fish/chicken moving order
more clearly - the first instance of trouble is with this
arrangement, found in Chicken Supreme, top(ish) centre:

 ###     In the original, if you take the bottom mask first, you lose
 #!!     when you take the other mask because the left two fish drop
 #!<     all the way, then the chicken moves and the other fish falls
 #@      on you.  So you have to take the top mask first on its own,
 #@  #   then push the top right fish, then take the other mask.
 #####

            In the Ovine version, though, as soon as you take the top
mask and move out again, the chicken moves left and lets the top right
fish fall on you - the top left fish doesn't move at all throughout.
You need an extra chicken to stop this happening (which is available
on the far right of the map).

It's also noticeable in Penultimate, where in the top right    #####
corner of the map the chicken has been removed, because        #@! #
otherwise the puzzle is impossible.  I guess they must have    ##! #
realised there was something wrong with their rules.  The       #@<#
final puzzle near the door also plays much simpler with the     #  #
Ovine rules - kind of a shame, that one took me ages to         #  #
figure out on the BBC version!

It is still kind of interesting though, as you have to think twice
about whether your "learned" solution will actually work.