Function: ffembed
Section: number_theoretical
C-Name: ffembed
Prototype: GG
Help: ffembed(a, b): given two elements a and b in finite fields, return a map
 embedding the definition field of a to the definition field of b.
Doc: given two finite fields elements $a$ and $b$, return a \var{map}
 embedding the definition field of $a$ to the definition field of $b$.
 Assume that the latter contains the former.
 \bprog
 ? a = ffgen([3,5],'a);
 ? b = ffgen([3,10],'b);
 ? m = ffembed(a, b);
 ? A = ffmap(m, a);
 ? minpoly(A) == minpoly(a)
 %5 = 1
 @eprog
