I try to plot such a thing:
f[x_, y_, z_] := Resolve[
Exists[i, i ∈ Integers && i > 0 && i < 10 && i^2 + x + y + z < 2]
]
RegionPlot3D[f[x, y, z], {x, -1, 1}, {y, -1, 1}, {z, -1, 1}]
But I get an error: "...must be a Boolean function". (I know that this function is very stupid, it should only acts as an example).
So even if the output of the function f[x,y,z] is True of False, Mathematica doesn't seem to recognize it as a Boolean function.
If I change the function to something which doesn't depend on x,y,z (only on i), then everything is fine.
f[x__?NumericQ] := Resolve[Exists[i, i \[Element] Integers && i > 0 && i < 10 && i^2 + Plus[x] < 2]]
$\endgroup$ – Kuba♦ Apr 21 '16 at 10:23