Function: alginvbasis
Section: algebras
C-Name: alginvbasis
Prototype: mG
Help: alginvbasis(al): basis of the natural order of the central simple algebra
 al in terms of the stored order.
Doc: Given an central simple algebra \var{al} output by \tet{alginit}, returns
 a $\Z$-basis of the natural order in \var{al} with respect to the
 order~${\cal O}_0$ stored in \var{al}.
 \bprog
 A = alginit(nfinit(y), [-1,-1]);
 ? alginvbasis(A)
 %2 =
 [1 0 0 -1]

 [0 1 0 -1]

 [0 0 1 -1]

 [0 0 0  2]
 @eprog
