#include<iostream>
#include<cstring>
#include<unordered_map>
#include<algorithm>

using namespace std;

const int N=100010; //数组开到100000 pat就ac了神奇。

int m,n;
int in[N],pre[N];
unordered_map<int,int> pos;
int p[N],depth[N];

int build(int il,int ir,int pl,int pr,int d)
{
    int root=pre[pl];
    int k=pos[root];

    depth[root]=d;

    if(il<k) p[build(il,k-1,pl+1,pl+1+(k-1-il),d+1)]=root;
    if(k<ir) p[build(k+1,ir,pl+1+(k-1-il)+1,pr,d+1)]=root;

    return root;
}
int main()
{
    cin>>m>>n;
    for(int i=0;i<n;i++)
    {
        cin>>pre[i];
        in[i]=pre[i];
    }

    sort(in,in+n);

    for(int i=0;i<n;i++)
        pos[in[i]]=i;


    build(0,n-1,0,n-1,0);

    while(m--)
    {
        int a,b;
        cin>>a>>b;

        if(pos.count(a)&&pos.count(b))
        {
            int x=a,y=b;

            while(a!=b)
                if(depth[a]<depth[b]) b=p[b];
                else a=p[a];

            if(a!=x&&b!=y) printf("LCA of %d and %d is %d.\n", x, y, a); 
            else if(a==x) printf("%d is an ancestor of %d.\n", x, y);
            else printf("%d is an ancestor of %d.\n", y, x);
        }
        else if(pos.count(a)==0&&pos.count(b)==0)
            printf("ERROR: %d and %d are not found.\n", a, b);
        else if(pos.count(a)==0)
            printf("ERROR: %d is not found.\n", a);
        else
            printf("ERROR: %d is not found.\n", b);
    }
    return 0;
}