a command that makes the turtle invisible
a reporter that stores the minimum y-coordinate for the world
a reporter that takes a list of numbers as input and reports the number with the maximum value in that list
a reporter that takes some values as input and reports a single list containing all of those values
a command that makes the turtle visible
a built-in turtle reporter that stores the y-coordinate of the turtle
a reporter that stores the maximum y-coordinate for the world
a reporter that reports the set of all turtles connected by a link to the turtle calling the reporter