The opening all three share

Stack the three nexus market mirrors published above one under another, which works neatly because they are the same length. Walk along them from the front, comparing one position at a time, stopping when any two disagree. You get 5 characters, spelling nexus. The gauge turns that into a fraction of the whole address, and the fraction is small.

That is the honest picture. A recognisable opening, followed by a great deal of material that has nothing in common at all. The last tile counts what is left after the shared part: 51 characters that carry every bit of the difference between one address and another.

An address is derived from a key, and the derivation is one way. You cannot pick the address you want. What you can do is generate keys over and over and keep one whose address happens to start with a string you like, which is why services that want a memorable opening end up with one and services that do not care end up with something unpronounceable.

A short opening like this one is cheap to produce. Not free, but cheap enough that it is a routine thing to do. The important consequence follows immediately: anybody willing to spend the same effort can produce an address that starts the same way. The opening is not owned, it is not registered, and nothing stops it being reused.

Most people check an address by reading the front. It is the natural thing to do, it is fast, and on this particular set it is the single weakest check available, because the front is exactly the part that has been deliberately made to look familiar.

Put it the other way round. If somebody wanted to hand you a string you would accept without much thought, the cheapest thing they could do is make it start the way the real ones start. The shared opening is therefore not evidence of anything. It is the part of the address you should weight least, not most.

This is not a warning about these three strings. It is a statement about where information lives in a string of this shape. Information lives where things differ, and things differ after position 6.

• Recognising at a glance that a string is meant to be one of this set, which is a filing question rather than a security one.
• Spotting a string that does not even attempt to look like one of them.
• Nothing else. It cannot separate one of the three from another, and it cannot separate any of them from a string made to resemble them.

It helps to stop thinking of an address as a name with a prefix and a suffix, and start thinking of it as 56 independent positions, of which 5 are shared decoration and 51 carry meaning. Under that framing the question "does it start correctly" stops feeling like a check at all, because you can see it only examines the decorated part.

The panel on front and back checks takes this further and puts a number on how much a typical glance actually reads.

Does a matching opening mean two addresses belong to the same operator?

No. It means somebody generated keys until they got that opening, and that is something anybody can do.

Is a longer chosen opening better?

It is more expensive to produce, which raises the bar slightly, but it does not change the logic. A chosen opening is chosen, and choice is available to anyone willing to spend the time.