# Draw only the top of the boundary of a function in Plot3d

So currently I have

via combining 3 Plot3D's in a show. My question is how can I make it so that the ONLY portion of that border highlighted green, is the "curving portion" in the xy plane, rather than the whole border...?

Related Code:

Code is a variation on

Show[Plot3D[{x^2 + y^2}, {x, 0, 1}, {y, 0, 1},
RegionFunction -> Function[{x, y, z}, x + y < 1]],
Plot3D[{0}, {x, 0, 1}, {y, 0, 1},
RegionFunction -> Function[{x, y, z}, x + y < 1],
BoundaryStyle -> Green]
]

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...... I just want to change which points are colored Green... right now all of the borders of the functions are colored Green. I don't think? RegionPlot is relevant –  Eiyrioü von Kauyf Mar 6 '13 at 23:37
Could you post the code for the plot so that we can see how the green curve is generated in the first place? –  Jens Mar 7 '13 at 0:20

## 1 Answer

 Show[Plot3D[{x^2 + y^2}, {x, 0, 1}, {y, 0, 1},
RegionFunction -> Function[{x, y, z}, x + y < 1]],
Plot3D[{0}, {x, 0, 1}, {y, 0, 1},
RegionFunction -> Function[{x, y, z}, x + y < 1],
Exclusions -> {{x + y == 1}},
ExclusionsStyle -> {None, Directive[Thick, Red]}], BoxRatios -> 1]


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Uhm that's Sec[x], not 1-x . also can I just put the function in to extend this for any function, e.g. a complication combination of x's and y's. ? –  Eiyrioü von Kauyf Mar 7 '13 at 5:27