require

• (require STRING)
  Makes the definitions of the specified module available in the current module (i.e., current file), where the string refers to a file relative to the enclosing file. The string is constrained in several ways to avoid problems with different path conventions on different platforms: a forward slash is a directory separator, "." always means the current directory, ".." always means the parent directory, path elements can use only "a"-"z" (uppercase or lowercase), "0"-"9", "-", "_", and ".", and the string cannot be empty or contain a leading or trailing slash.
• (require (lib STRING STRING ...))
  Access a file in an installed library, making its definitions available in the current module (i.e., current file). The first string names the library file, and the remaining strings name the collection (and sub-collection, and so on) where the file is installed. Each string is constrained in the same way as for the (require STRING) form.
• (require (planet STRING (STRING STRING NUMBER NUMBER)))
  Accesses a library that is distributed on the internet via the PLaneT server, making it definitions available in the current module (i.e., current file).

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