Yes, the function is exist.
Since the function P is one - to - one function.
Because the each population of U.S. corresponds to exactly one particular year.
![\"\"](\"/userfiles/image/steps_images/step1.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=ef452840db21ad56882db3c98d680447.png\")
is exist.![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
![\"\"](\"plugins/fckeditor_wiris/integration/showimage.php?formula=ef452840db21ad56882db3c98d680447.png\")
is exist.