Hi I have started a new subject this week called Topology, and it a bit harder than the stuff that I am used too, but anyway
We have metric space called where two and . Then I need to show that there exists open sets
which statifies that 1) 2) and 3)
Firstly I know that the definition of open set or ball is as follows
In other words: A set U is considered open if there for every element in the set is the center of an open ball of the set.
I also know from the metric subject field that if x,y are point in the set T and if they a then d(x,y) > 0.
So the way to show 1) and possible 2) isn't that to claim that for set to be open I must show that every point m_j on that set will be the center of an open ball?
I can see all the definitions that I need in my head I just need some assistance to connect them
Cheers
Julie
For you convience my textbook is Apostol "Mathematical Analysis second edition".
On page 49 there is not exactly a theorem but it states
Let a be a point in and let r be a possitive number then th set of all points x in such that
is called an open n-ball of radius and center a, and I et that epsilon and delta are some sort measures which are used to determen what happens at a.
There is a definition on the same page which states that every interior point a of a set S can b surrounded by an "n-ball" and any set containing a ball with cente a is refered to as a neighbourhood of a.
So basicly my task is to show there exist a neighbourhood around m1 which only holds m1 and not m2?
This may be stupid question but I know the axioms of metric
there is one which states d(x,y) > 0 -> and you choose a small delta and bit larger epsilon and the bigger delta gets the smaller epsilon until it reaches m1 and thusly m1 does not contain m2?
I am not trying to sound stupid or anything but its just then I get these generalized assignments I crash and burn, but then there is assignment with numbers then everything is fine.
I don't suppose you could explain to me in a example on how is much proceed? then everything works much better
Well, its not "stupid" but it is confused. In the first place, while responses above have mentioned " , no one has said anything about an " so I don't know where you got that. The point is to show a neighborhood about each point that is disjoint from the other. Making small should do that.
Also "m1 does not contain m2" makes no sense. m1 and m2 are points, not sets.