Function: core
Section: number_theoretical
C-Name: core0
Prototype: GD0,L,
Help: core(n,{flag=0}): unique squarefree integer d
 dividing n such that n/d is a square. If (optional) flag is non-null, output
 the two-component row vector [d,f], where d is the unique squarefree integer
 dividing n such that n/d=f^2 is a square.
Doc: if $n$ is an integer written as
 $n=df^2$ with $d$ squarefree, returns $d$. If $\fl$ is non-zero,
 returns the two-element row vector $[d,f]$. By convention, we write $0 = 0
 \times 1^2$, so \kbd{core(0, 1)} returns $[0,1]$.

Variant: Also available are \fun{GEN}{core}{GEN n} ($\fl = 0$) and
 \fun{GEN}{core2}{GEN n} ($\fl = 1$)
