> restart:

> with (plottools):

> r:=sqrt(8)/2:

> a1:=sphere([1,1,1],r):

> a2:=sphere([1,-1,-1],r):

> a3:=sphere([-1,-1,1],r):

> a4:=sphere([-1,1,-1],r):

> with (plots):

Warning, the name changecoords has been redefined

> display (a1,a2,a3,a4,scaling=constrained);