Function: znorder
Section: number_theoretical
C-Name: znorder
Prototype: GDG
Help: znorder(x,{o}): order of the integermod x in (Z/nZ)*.
 Optional o represents a multiple of the order of the element.
Description:
 (gen):int             order($1)
 (gen,):int            order($1)
 (gen,int):int         znorder($1, $2)
Doc: $x$ must be an integer mod $n$, and the
 result is the order of $x$ in the multiplicative group $(\Z/n\Z)^*$. Returns
 an error if $x$ is not invertible.
 The parameter o, if present, represents a non-zero
 multiple of the order of $x$, see \secref{se:DLfun}; the preferred format for
 this parameter is \kbd{[ord, factor(ord)]}, where \kbd{ord = eulerphi(n)}
 is the cardinality of the group.
Variant: Also available is \fun{GEN}{order}{GEN x}.
