How can I add lines that demarcate the different regions of the following 3D plot:
Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, -8, 8}]
To give you an idea of what I have in mind I have added the lines and descriptions in the 3D plot in paint; now I want to know how to do it directly in Mathematica.