# File:R2 top group preimage of 1 to -1 epsilon 0.25 steps 0.125.gif

R2_top_group_preimage_of_1_to_-1_epsilon_0.25_steps_0.125.gif(256 × 128 pixels, file size: 48 KB, MIME type: image/gif, looped, 35 frames, 7.0 s)

This is an example image for showing that [ilmath](\mathbb{R}-\{0\},\times)[/ilmath] is a topological group. Consider [ilmath]m:(\mathbb{R}-\{0\})\times(\mathbb{R}-\{0\})\rightarrow\mathbb{R}-\{0\} [/ilmath] given by [ilmath]m:(x,y)\mapsto xy[/ilmath], as the example shows [ilmath]m[/ilmath] is continuous (when [ilmath](\mathbb{R}-\{0\})^2 [/ilmath] is considered with the product topology), an important step in doing that is showing that:

• Given an open ball, [ilmath]B_\epsilon(c)[/ilmath] which is, in this case, the open interval [ilmath](c-\epsilon,c+\epsilon)[/ilmath] we must show that the preimage is open (among other things of course).

This image shows the preimage of [ilmath](c-\epsilon,c+\epsilon)[/ilmath] as [ilmath]c[/ilmath] goes from [ilmath]-1[/ilmath] to [ilmath]1[/ilmath] in steps of [ilmath]0.125[/ilmath]. For [ilmath]\epsilon:=0.25[/ilmath].

You can see for [ilmath]c=0[/ilmath] the image is symmetric about the [ilmath]x[/ilmath]-axis, [ilmath]y[/ilmath]-axis, [ilmath]y=x[/ilmath] line and [ilmath]y=-x[/ilmath] line and forms like a 4-point star shape. This technically isn't in the space we're dealing with, however we do see the preimage of [ilmath](-0.25,0.25)[/ilmath] in the space.

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Date/Time Thumbnail Dimensions User current 03:11, 8 August 2016 256 × 128 (48 KB) Alec (Talk | contribs)
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