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.
