How do I find analytical apexes of a region? [duplicate]

Question

I have a set of inequalities that plot to the region given below, how do I find the analytical apexes that shape this region?

Reg = RegionPlot3D[
  1 >= a >= b >= 1 - b >= 1 - a >= 0 && 
  1 >= δ >= a - δ >= b - δ >= 1 - a - b + δ >= 0, 
  {a, 1/2, 1}, {b, 1/2, 1}, {δ, 0, 1},
  PlotPoints -> 200, MaxRecursion -> 10]

Answer 1

The region is surrounded by four planes：1 - x - y + z = 0, x = y, 1 - x - 2 y + 2 z = 0 and x = 2 z. We can find the crossover points of them.

Show[Reg, 
 Graphics3D[{PointSize[Large], Red, 
   Point[{x, y, z} /. 
     Catenate[
      Solve[#, {x, y, z}] & /@ 
       Subsets[{1 - x - y + z == 0, x == y, 1 - x - 2 y + 2 z == 0, 
         x == 2 z}, {3}]]]}]]