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@Steve237

```
RegionPlot3D[
 And @@ {x - 1/2 <= y <= x + 1/2, x - 1/2 <= z <= x + 1/2 , 
   0 <= x <= 1, 0 <= y <= 1, 0 <= z <= 1}, {x, 0, 1}, {y, 0, 1}, {z, 
  0, 1}, PlotPoints -> 80, PlotStyle -> Opacity[0.2], Mesh -> None, 
 BoundaryStyle -> Blue]
```