1) For all X1 and all X2, such that X1 and X2 are
elements of the set of all real numbers, X1=X2 implies that F(X1)=F(X2). In other words, if you put the same number into your function that
you already put in you are unlikely to get a different result.
2) Jack did not believe the waitress when she told him that his martini came to $9.37 after tax so he did some discrete math under his coat to
double check her.