import tube;
import graph3;

size(7.5cm,0);

currentprojection=perspective(7,10,3);
currentlight=light(8,10,2);

real a=5;
path3 g1=(a,-a,0)--(a,a,0)..(0,a,a)..(-a,a,0)
         --(-a,-a,0)--(0,-a,a)--cycle;

draw(tube(g1,scale(a/10)*unitcircle),red);

limits((-a,-a,-a),(1.5a,1.5a,1.5a));
xaxis3("$x$",Arrow3);
yaxis3("$y$",Arrow3);
zaxis3("$z$",Arrow3);