Code with RegionDimension and ImplicitRegion doesn't work?

Questions
1

Based on the example here, I tried the following code snippet, but it doesn’t work at all:

In[143]:= RegionDimension@ImplicitRegion[x == 1 && y == 2 || (x < 1 && y < 2), {x, y}]
RegionDimension@ImplicitRegion[x == 1 && y == 2, {x, y}]

Out[143]= RegionDimension[
 ImplicitRegion[(x == 1 && y == 2) || (x < 1 && y < 2), {x, y}]]

Out[144]= RegionDimension[ImplicitRegion[x == 1 && y == 2, {x, y}]]

As represented on stackoverflow, the posted answer there has the following output:

Selection_133.png
Selection_133.png1227×960 102 KB

I don’t understand why I run the same code and get nothing.

Regards,
Zhao

2

I get the same answer as Stack Overflow. x or y must be Set to something. Try Clear[x, y].

3

Yes. It does the trick.