Function: algisquatalg
Section: algebras
C-Name: algisquatalg
Prototype: G
Help: algisquatalg(al): returns [a,b] if al was constructed as the quaternion
 algebra (a,b)_F, and 0 otherwise.
Doc: Given a central simple algebra \var{al} over a field $F$, output by
 \tet{alginit}, returns the \typ{VEC} $[a,b]$ if \var{al} was constructed as a
 quaternion algebra~$(a,b)_F$, and~$0$ otherwise.
 \bprog
 ? nf = nfinit(y^2-2);
 ? pr = idealprimedec(nf,2)[1];
 ? al = alginit(nf, [[pr],[1,0]]); \\ quaternion algebra from ramification
 ? algisquatalg(al)
 % = [y + 1, y + 1]
 @eprog
