A few days ago, I asked about the continuity of a function, in regards to a problem on my homework. Something still seems wrong, even though today my professor insisted that the given definitions are correct. Look here: http://www.math.washington.edu/~sullivan/3261_sp10.pdf" A function f(x,y) is continuous at a point (x0,y0) if f(x,y) is defined at (x0,y0), .... A function f(x,y) is discontinuous at a point (x0,y0) if f(x,y) is defined at (x0,y0), ..... So if a function isn't defined, then it is neither continuous or discontinuous????????