Procedure from library zeroset.lib (see zeroset_lib).
zeroset.lib
EGCD(f, g); where f,g are polynomials
compute the polynomial gcd of f and g over Q(a)[x]
polynomial h s.t. h is a greatest common divisor of f and g (not nec. monic)
basering = Q(a)[t]
Example:
LIB "zeroset.lib"; ring R = (0,a), x, lp; minpoly = a2+1; poly f = x4 - 1; poly g = x2 - 2*a*x - 1; EGCD(f, g); → (-4a)*x-4