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Homework Help: Topology: Boundary

  1. Sep 29, 2010 #1
    Determine the boundary of A.

    A= (-1,1) U {2} with the lower limit topology on R

    What I know is that the topology defines open sets as those of the form [a,b). In this case, if they want an interval in the form of [a,b) for the interior, then it comes to mind that [0,1) would be the interior since [-1,1) is not contained in A. The closure of the set also baffles me a little, because I'd think that would just be [-1, 2) since R - [-1, 2) = (-infty, -1) U [2, infty) which is an open set in R with the lower limit topology, so I'd figure that [-1, 2) is closed in the lower limit topology.

    Is it possible that anybody can help me to figure out the interior of A or at least push me in the right direction?
  2. jcsd
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