intervals for wxmaxima

 
In this file,

 http://www.cs.berkeley.edu/~fateman/generic/int4max.lisp

is  rudimentary interval package.  it uses facilities in nnformat for
display, so that must be read in first.

try z:interval[-1,1];
y:interval[-1,1];

z*z;

ieval(z*z);
ieval(z*y);

ieval(1/2);