//Zory-2019
#include<bits/stdc++.h>
using namespace std;
namespace mine
{
    typedef long long ll;
    #define pr pair<int,int>
    #define FR first
    #define SE second
    #define MP make_pair
    #define PB push_back
    #define vc vector
    #define all(x) (x).begin(),(x).end()
    #define sz(x) ((int)(x).size())
    #define bin(x) (1ll<<(x))
    #define GG(x) if(x) {puts("error");exit(666);}
    #define fo(i,l,r) for(int i=(l),I=(r);i<=I;i++)
    #define fd(i,r,l) for(int i=(r),I=(l);i>=I;i--)
    ll qread()
    {
        ll ans=0,f=1;char c=getchar();
        while(c<'0' or c>'9') {if(c=='-')f=-1;c=getchar();}
        while('0'<=c and c<='9') ans=ans*10+c-'0',c=getchar();
        return ans*f;
    }
    void write(ll num)
    {
        if(num<0) putchar('-'),num=-num;
        if(num>=10) write(num/10);
        putchar('0'+num%10);
    }
    void write1(ll num){write(num);putchar(' ');}
    void write2(ll num){write(num);putchar('\n');}
    template<typename T> void chmax(T &x,const T y) {x=(x>y?x:y);}
    template<typename T> void chmin(T &x,const T y) {x=(x<y?x:y);}
    ll gcd(ll x,ll y){return y?gcd(y,x%y):x;}

    const int INF=0x3f3f3f3f;
    const int MOD=998244353;
    int mm(const int x){return x>=MOD?x-MOD:x;}
    template<typename T> void add(T &x,const int &y){x=(x+y>=MOD?x+y-MOD:x+y);}
    ll qpower(ll x,ll e,int mod=MOD){ll ans=1;GG(e<0)while(e){if(e&1)ans=ans*x%mod;x=x*x%mod;e>>=1;}return ans;}
    ll invm(ll x){return qpower(x,MOD-2);}
    const int N=5e4+10,T=256;

    namespace Trie
    {
        int id=1,son[T*17][2];void clear(){fo(i,0,id)son[i][0]=son[i][1]=0;id=1;}
        void insert(int num)
        {
            int now=1;
            fd(i,15,0)
            {
                int wt=(num>>i)&1;
                if(!son[now][wt]) son[now][wt]=++id;
                now=son[now][wt];
            }
        }
        int ask(int num)
        {
            int now=1,ans=0;
            fd(i,15,0)
            {
                int wt=(num>>i)&1;wt^=1;
                if(!son[now][wt]) wt^=1; else ans+=bin(i);
                now=son[now][wt];
            }
            return ans;
        }
    };

    int ff[N];vc<int> to[N];
    int n,hh[N][N/T+1],a[N],dep[N],anc[N];//debug 忘记+1，原地暴毙
    void pre(int x,int fa)
    {
        ff[x]=fa;dep[x]=dep[fa]+1;
        Trie::clear();int now=x;
        for(int dis=0;dis<T and now>0;dis++,now=ff[now]) Trie::insert(a[now]^dis);
        anc[x]=now;
        fo(t,0,n/T) hh[x][t]=Trie::ask(t*T);
        for(auto y:to[x]) if(y!=fa) pre(y,x);
    }
	void main()
	{
        n=qread();int q=qread();fo(i,1,n) a[i]=qread();
        fo(i,2,n) {int x=qread(),y=qread();to[x].PB(y);to[y].PB(x);}
        pre(1,0);
        while(q--)//x->y
        {
            int y=qread(),x=qread(),ans=a[y]^(dep[x]-dep[y]),z=x;
            while(dep[z]-T+1>=dep[y]) chmax(ans,hh[z][(dep[x]-dep[z])/T]),z=anc[z];
            while(dep[z]>=dep[y]) chmax(ans,a[z]^(dep[x]-dep[z])),z=ff[z];
            write2(ans);
        }
	}
};//(ans+MOD)%MOD
signed main()
{
    // freopen("a.in","r",stdin);
    srand(time(0));
    mine::main();
}