Maxima Function
gfactor (expr)
Factors the polynomial expr over the Gaussian integers
(that is, the integers with the imaginary unit %i adjoined).
This is like factor (expr, a^2+1) where a is %i.
Example:
(%i1) gfactor (x^4 - 1); (%o1) (x - 1) (x + 1) (x - %i) (x + %i)