Except for conditional relations, relations are automatically reversible. Defining another verb to mean the reversed relation can make it easier to access the info in the other direction…
The Inn is a room.
An inn-table is a kind of thing.
The table is an inn-table in the Inn.
A customer is a kind of person.
Bob is a customer in the Inn.
Sitting relates various customers to one inn-table.
The verb to sit at means the sitting relation.
The verb to seat means the reversed sitting relation.
The table seats Bob.
If the verb you associate with a relation is single-word, Inform automatically creates a to be <verb>ed by verb meaning the reversed relation (as well as a to be <verb>ing alias for the regular relation).
Ownership relates one person to various things.
The verb to own means the ownership relation.
Bob owns the wristwatch.
when play begins:
if the wristwatch is owned by Bob, say "tick tock.";
if Bob is owning the wristwatch, say "tock tick.";
<=> is just something the relations debugging command uses in output. It’s not Inform code.