The site is full of 'spoilers' for the book

Living Labyrinth

by Ian Stewart and Tim Poston

If you can't read St Matthew's Gospel because St Mark gave away the resurrection, don't explore further.

I like background on books:
let me in, and do not warn me again

or Go to where I can get the book.

Concordat of Habitable Exoplanets

This powerful organisation's central function is to limit conflict by controlling Da Silva traffic between star systems. (Between habitats around one star, travel is mostly slower than light, and locally controlled). It strictly controls mahabhavium, which is essential for Da Silva drives. Drives are licenced, can be nulled via the Concordat-controlled grid.

Since simquakes can cut off a planet for a locally-experienced century from contact with other solar systems, planetary governments must be robust in case of isolation, with local enforcement of locally accepted laws. This requires considerable local autonomy, and (in combination with differences in history and environment) variability.

Human travel is largely unregulated between Core worlds, though tracked. Citizens of Associate worlds need to pass toleration and flexibility tests to travel to Core worlds, and more severe ones to travel to other Associate worlds, whose folk are less cosmopolitan. Fringe-worlders are more limited still.

The most visible privilege of Starfolk status is freedom to go anywhere. The Valkyrie team are still probationary Starfolk, while on Qish, but 'probationary' is sometimes dropped for courtesy or brevity.

Note that this system is one of travel control by the Concordat, not a visa system managed by individual governments.

The Concordat discourages interstellar censorship, because it builds up stresses and potential culturequakes, but is not dogmatic about this.