The Peter - visible element represents the flag of Peter's visibility. If Peter is visible, his motion over the sheet is animated according to the definition of the Peter sprite's definition. Peter's visibility being switched off, Peter's motions over the sheet are executed immediately.

 

The element of Peter's visibility can be treated as a normal logic variable. By using it in a logic term it can be tested, if Peter is visible. Under "visibility" is understood the possibility of doing animations of the Peter sprite independently on whether Peter is present in the sheet visible portion. By using the visibility element as a command its value may be set by means of a logic term, thus switching Peter's visibility on or off.  In case a preceding command to shift to a specified coordinate has been given he will first finish the shift before the visibility can be switched on or off.