It is thought to be part of the shell script code like
if [ -f file ]

... have you have ever wondered, why a bracket has an option ?    :)

 

 Is this number prime?
 

 ...me too.
Are there any users guides for Amethyst out there?
 

 Think of a situation, in which youy may feel to have failed of in which you have succeded as of an scientific experiment. You have created a theory of how something may work and in this experiment you put your theorie to  an test to proof it write or wrong.

For a scientist a disproofed theory is not a failure - it is just a different way to gain knowledge how things work.

The only important thing for you is to gain knowledge out of this experiment.

HTH!