### Plotting an inequality in 3D region

Ideally I would like to plot a region in 3D space which is defined by a bunch of inequalities. For example let us consider the region $R$ defined by $ { (x,y, z): x ~~<= ~~\le 0 \text{ and } y ~~<= ~~\le 0 \text{ and } x+y ~~<= ~~\le z } $.

I am wondering what would be an easier way to do it.

With my limited knowledge I came up with these two approaches.

*Approach 1 :* Generate points in this region and plot them in 3D. Is there a way to extend the function in ` region_plot () `

that generates plot points for my needs?

*Approach 2 :* Concatenate implicit -3D plots of functions of the form $ x + y - (z+t) $, where $t$ is a small positive parameter, for different values of $t$. Then plot all these simultaneously.

I would appreciate any alternate way to do this or any improvements on these approaches.

Thank you for your time in advance.