a reporter that reports a random y-coordinate in the world window
a reporter that reports a random x-coordinate in the world window
a command that takes a number and a set of commands as input and repeats that set of commands the specified number of times
a reporter that reports the current value of the tick counter
a built-in turtle (and link) variable that stores the set of all turtles (or links) that are the same breed as the turtle (or link) calling the reporter
a command that takes a value as input and prints that value in the Command Center
a value that indicates that no agent was found when using one-of, max-one-of, etc.
a command that makes a link invisible
