Contributed by
Dan Shawin
About a mobile city that must tap its
power from a mysterious `optimum point', which is less effective for
their engines as it gets more distant. Weird distortion of the
surrounding world is based on hyperbolic functions. Parts of the yarn
get pretty weird, but it is still a story well told.

Contributed by
Anonymous
The author seems to change the direction of the plot towards the last third of the book but its still worth a read.

Contributed by
Lapo Fanciullo
Mathematics is not central to this novel, but there's at least a fascinating idea: the story is set on a planet with a negative curvature. More precisely, it's the solid of revolution of a rectangular hyperbola spun around one of its asymptotes (the book uses less precise terminology, but it's clear anyway what it's talking about). This is revealed to be an approximation, or the planet would be infinite (since it rotates around its symmetry axis, the world "ends" before the speed of rotation exceeds that of light).
The "optimum point", by the way, is placed on the vertice of the hyperbola, but since the planet's ground slides the city never reaches it once and for all, hence the need for it to move on rails.
There's a twist concerning the planet's shape towards the end of the book, but since it's a major spoiler and a bit of a letdown for mathsavvy readers, I won't write about it.

Contributed by
JeanPierre Zurru
Some years ago i had the opportunity to talk with Priest at a signing. I mentionned the mathematical quality of 'The inverted world", and how the universe could be assimilated to a pseudoshpere. Priest told me he was not aware of this and had no clue as to the underlying mathematical notions we can find in his book
.
He found it interesting and suggested someone could try to write something about it.

JeanPierre, are you certain that the author claimed to be unaware of any of the mathematical interpretations that this story obviously lends itself to? That seems unlikely to me. I know that it is sometimes possible for a mathematically inclined reader to see mathematical aspects of a work of fiction that were not apparent to the author, but in this case it seems clear that they were intentional. I wonder if, perhaps, you might have been talking about one particular detail or concept of which he was not previously aware.
Contributed by
JeanPierre Zurru
I reckon i might have not caught the full meaning of what Priest said since English is not my native language, or he might have been ironic toward a fan asking for the thousandth time the same question about the maths in the Inverted world.
However, as far as i remember (t'was about 10 years ago), if he was serious, i really think he meant he did not care about the maths when he wrote the book. I remember asking him about the mathematical content of the book in a general way. I did not mention directly the pseudosphere or hyperbolic geometry.

