Suppose I have, if you look at this; suppose this is on the boundary, this is on the surface, when we say A infinity, this is called B. This is C, this is D. I will call it infinity. So, there are 4 vertices, 2 vertices are infinity and 2 are at some point finite point and this is this side is closed. So, there are 3 sides which are closed; one side it is open up to infinity. Now if I just say that 2 straight lines; suppose this is one boundary this is another boundary, and suppose this is called A infinity to B infinity and this is C infinity to D infinity. This is a rectangle; this is a kind of rectangle whose vertices are positive infinity. This is negative infinity and they both are certain distance apart. Suppose A here also you can say suppose there distance apart is A, but in this case this side is closed, this side is extended up to infinity. On the other hand, I will go to third case. Let us look at a triangle. This triangle, I say that A infinity this point is at infinity and I have B and this is