void merge(Item a[], int left, int mid, int right){
int N = right-left+1, i;
Item temp[N];
mergeAB(temp,a+left,mid-left+1,a+mid+1,right-mid);
for (i=0; i<N; i++){
a[left+i] = temp[i];
}
}
void mergesortABr(Item a[], Item b[], int l, int r)
{
if (r-l <= 10) {
insertion(a, l, r);
return;
}
int m = (l+r)/2;
mergesortABr(b, a, l, m);
mergesortABr(b, a, m+1, r);
mergeAB(a+l, b+l, m-l+1, b+m+1, r-m);
}