We can use import to reference definitions in other files.
Thus one file can be viewed as a module of definitions.
For example,
  • The current file is located at "/module/",
  • we can use relative path "../datatypes/", to locate "/module/database/",
  • in which a datatype called Nat is defined (we will talk about Nat in the following chapters),
  • and we import this definition.
Under some URLs, there are files.
We can even import from them.
Since the name Nat is already imported, and we can not redefine names. We use Nat as NatFromURL to rename the imported definition.