output --Command, one input. Abbreviation: op
     This command is used in a user procedure which is meant to be an
     operation. The input to this command becomes the output from the user
     procedure. Please don't be confused by the fact that the user
     procedure is an operation, while the output primitive procedure is a
     command used in that procedure. Example:

     to nickname :person
     if equalp :person [Peter Parker] [output "Spiderman]
     if equalp :person [Lamont Cranston] [output "Shadow]
     output first :person
     end