# How to draw an intersection between a sphere and a plane in asymptote

I'm learning to use asymptote. I'm trying to draw an intersection between a sphere and a plane. Below I post the code. There do not seem to be any errors in the concept: I draw the sphere, the back and front equator and the horizontal plane. Why does the equator in not on the horizontal plane?

The code:

import solids;
import graph3;
import three;
size(5cm);

currentprojection=orthographic(10,5,2);
real t = 1;
triple p0 =(t,t,0), p1=(-t,t,0), p2 = (-t,t,0), p3 = (t,-t,0);
nslice=4*nslice;
revolution b=sphere(O,1);
draw(surface(b),paleblue+opacity(.5));
skeleton s;
b.transverse(s,reltime(b.g,0.5),P=currentprojection);
draw(s.transverse.back,yellow);
draw(s.transverse.front,yellow);
draw(surface(p0--p1--p2--p3--cycle),brown);


You are doing everything right except that you forgot to flip a sign in p2.

\documentclass{standalone}
\usepackage{asypictureB}
\begin{document}
\begin{asypicture}{name=AsyPlot}
import solids;
import graph3;
import three;
size(5cm);

currentprojection=orthographic(10,5,2);
real t = 1;
triple p0 =(t,t,0), p1=(-t,t,0), p2 = (-t,-t,0), p3 = (t,-t,0); //adjusted p2
nslice=4*nslice;
revolution b=sphere(O,1);
draw(surface(b),paleblue+opacity(.5));
skeleton s;
b.transverse(s,reltime(b.g,0.5),P=currentprojection);
draw(s.transverse.back,yellow);
draw(s.transverse.front,yellow);
draw(surface(p0--p1--p2--p3--cycle),brown);
\end{asypicture}
\end{document} 