+Troupe is an esolang designed by Chris Pressey on June 25, 2012, in Winnipeg,
+The name of this esolang is **Troupe** in the UK and Canada and Australia,
+but in the USA, where they drop the "u" in words where it follows an "o", its
+We have a troupe of hedgehogs. Each has a position, a colour (in the USA:
+color), a possible hedgehog to its left, and a possible hedgehog to its
+right. In this troupe, there is only one hedgehog which has no hedgehog to
+its left, and only one hedgehog which has no hedgehog to its right, and the
+following is true: for each hedgehog X, if Y is the hedgehog to X's right
+(resp. left), then X is the hedgehog to Y's left (resp. right). (i.e. the
+hedgehogs are in a line formation.)
+For some hedgehog X, the hedgehog to X's left and the hedgehog to X's right
+are the *neighbours* (in the USA: *neighbors*) of X.
+We may say that a hedgehog is "one of the hedgehogs to the left" (resp.
+"right") of some other hedgehog; the meaning of this should be evident -- it
+is just the transitive closure of "to its left" (resp. right).
+All hedgehogs share a fixed speed at which they move (when they move), and a
+fixed radius. Also, the troupe consists of a finite number of hedgehogs at
+all times, and their colours come from a finite set of possible colours that
+can be distinguished from one another. (And that there is one distinguished
+"default" colour, which we will arbitrarily call "white".)
+In the troupe, at any given time, there is either exactly one *leader*
+hedgehog, or exactly one *leader-elect* hedgehog; never both and never
+The leader hedgehog, when it exists, has a velocity. It moves through space
+with this velocity, changing its position. All other hedgehogs in the troupe
+try to "follow" it, which means the following:
+Each hedgehog moves to minimize the distance between it and one of its
+neighbours (up to a certain point: if the distance between it and its
+neighbour is less than three times the hedgehog radius, it does not bother
+The neighbour it moves toward is the hedgehog on its left (resp. right), if
+the leader is one of the hedgehogs to the left (resp. right).
+We also have a set of faery rings. Each ring has a fixed position, radius,
+inner colour, and outer colour; it optionally has a signpost, a unit vector
+pointing in any direction; and it optionally has an orientation, which is
+either clockwise or counterclockwise.
+Faery rings may not intersect each other *except* if both rings have
+precisely the same position and radius *and* if they have different outer
+colours. (They may have the same inner colour.)
+When a leader hedgehog intersects a faery ring (i.e. when the distance
+between the hedgehog is less than the sum of the hedgehog radius and the
+particular ring's radius), and if the outer colour of the faery ring is the
+same as the colour of the leader hedgehog, the following things happen, in
+* The faery ring, and all faery rings which intersect it, become temporarily
+ inactive, in that intersection with a hedgehog does not set off this same
+ sequence of events until it becomes active again.
+* The leader hedgehog's colour is changed to the inner colour of the faery
+* If the faery ring has a counterclockwise (resp. clockwise) orientation,
+ then the hedgehog to the leader hedgehog's left (resp. right) becomes
+ the leader-elect hedgehog.
+ (If there *is* no hedgehog to the left (resp. right) of the leader
+ hedgehog, then one pops into existence, at the same position as the
+ leader hedgehog, and with a white colouring; and it becomes the
+ leader-elect hedgehog.)
+ When the set of hedgehogs has a leader-elect, the leader-elect moves to
+ minimize its distance to the faery ring that made it leader-elect, and
+ all other hedgehogs follow the leader-elect, as described above.
+ Once the leader-elect hedgehog intersects the faery ring which made it
+ the leader-elect (which it will eventually, as it moves to minimize the
+ distance), it becomes the leader hedgehog.
+* If the faery ring has a signpost, the leader hedgehog is given a velocity
+ in accordance with the direction of the signpost.
+* Once the leader hedgehog no longer intersects the faery ring, the faery
+ ring, and all rings that it intersects, become active once again.
+There are also any number of hills, each with a fixed position and radius.
+These serve as goals; when the leader hedgehog reaches a goal hill, the
+troupe's quest is over, and they are free to break formation and nibble on
+clover or whatever it is that hedgehogs do for fun.
+Part IV. Computational Class
+The system outlined above should be Turing-complete, as it maps quite
+readily to the definition of a Turing machine.
+The line of hedgehogs serves as the tape, with their colours being symbols on
+the tape, and the leader being the tape head.
+The faery rings implement state transition rules, or rather, the parts of
+transition rules that say "If the symbol on the tape is..." (which in our
+system translates to "If the leader hedgehog is coloured...") Overlapped
+faery rings of all possible colours make for a traditional transition rule.
+The state itself is encoded by the leader's position and velocity and which
+faery ring they're headed toward next. As long as the faery rings are
+arranged appropriately, we can guarantee that, when the leader hedgehog
+leaves a faery ring, possibly with a new velocity, it is bound to intersect
+another faery ring eventually. An example of an appropriate arrangement is:
+* The signpost in each faery ring points in a cardinal direction.
+* All faery rings have the same radius.
+* For each faery ring, there is another faery ring which shares at least
+ one of its coordinates.
+Finally, the hills serve as halt states.
+We can certainly allow for the presence of elements in this world which
+either do not affect the property of being Turing-complete, or if they do,
+are not required to be present in any particular instance of the world.
+A rest area has a fixed position and radius.
+If the leader hedgehog enters a rest area, it does not move until no
+hedgehog in the troupe is impelled to move (i.e. until all hedgehogs are
+within three times the hedgehog-radius of another hedgehog.) This allows
+the troupe to "catch up" with the leader.
+This system is, of course, crying out to be implemented with a visual
+animation of the hedgehogs moving around, possibly in a Java applet, or
+We have not specified the dimensionality of the space in which these things
+exist; certainly, two dimensions would be a reasonable restriction,
+especially for an animated visual implementation.
+The system probably continues to be Turing-complete in one dimension, but
+I have not convinced myself of that. One of the things that allows this
+(if it is true) is that hedgehogs are happily allowed to pass right through
+other hedgehogs as if they didn't exist. If this was not true, then a one-
+dimensional realization of this world is probably not Turing-complete.
+In two dimensions, however, even if hedgehogs are not allowed to pass
+through each other, the system is still Turing-complete (cf. Beturing),
+although we might have to add one proviso. Since, in order to really be
+Turing-complete, the troupe of hedgehogs needs to be able to grow without
+bound, it might become intractably large. When the leader hedgehog is not
+able to make progress because of some other hedgehog in its way, it should
+act as if it entered a rest area. Also, we may require some "jitter" be
+introduced in follower hedgehog movements, lest they get stuck.
+We may want to go further, and allow the space itself to expand whenever a
+hedgehog is added to the troupe -- so long as all the relative directions
+between things are preserved, this should not affect the outcome.
+(The idea for this system came to me sort of all at once when I was thinking
+about Beturing, specifically that Beturing doesn't address the tape at all
+in its concerns about wire-crossing. I mean, don't we have to communicate
+to the tape somehow, and might not those lines of communicate cross other
+lines of communication? Then I thought, well, it can assume that the tape
+is *inside* the state pointer somehow. And the rest followed more-or-less
+We have not specified, either, whether this system should be implemented with
+a discrete simulation or a continuous simulation. Actually, either should
+work, I think; and a continuous simulation would be somewhat interesting, if
+only for the fact that most language interpreters are discrete. A continuous
+simulation would use real numbers to measure both duration and distance, and
+real analysis techniques to discover the evolution of the system. Motion of
+the hedgehogs would be genuinely continuous except for the points where their
+velocities change due to one hedgehog approaching another too closely, etc.