#include <bits/stdc++.h>
using namespace std;
const int maxn = 50010;
int n, Q, f[maxn][260], g[maxn], fa[maxn], a[maxn], head[maxn], to[maxn * 2],
    nextt[maxn * 2], tot = 1, deep[maxn], Tot;
struct node {
  int tr[2];
  void clear() { memset(tr, 0, sizeof(tr)); }
} e[300010];
void add(int x, int y) {
  to[tot] = y;
  nextt[tot] = head[x];
  head[x] = tot++;
}
void dfs(int u, int faa) {
  deep[u] = deep[faa] + 1;
  fa[u] = faa;
  for (int i = head[u]; i; i = nextt[i]) {
    int v = to[i];
    if (v == faa) continue;
    dfs(v, u);
  }
}
void insert(int x) {
  int u = 1;
  for (int i = 16; i >= 0; i--) {
    int temp = (x >> i & 1);
    if (!e[u].tr[temp]) {
      e[u].tr[temp] = ++Tot;
      e[Tot].clear();
    }
    u = e[u].tr[temp];
  }
}
int query(int x) {
  int u = 1, res = 0;
  for (int i = 16; i >= 0; i--) {
    int temp = (x >> i & 1);
    if (e[u].tr[temp ^ 1]) {
      res |= (1 << i);
      u = e[u].tr[temp ^ 1];
    } else
      u = e[u].tr[temp];
  }
  return res;
}
void prework(int x) {
  e[Tot = 1].clear();
  int u = x;
  for (int i = 0;; i++) {
    if (u == g[x]) break;
    insert(i ^ a[u]);
    u = fa[u];
  }
  for (int i = 0; i <= n / 256; i++) f[x][i] = query(i * 256);
}
void solve(int x, int y) {
  int temp = 0, res = 0;
  while (deep[y] - deep[x] >= 256) {
    res = max(res, f[y][temp]);
    y = g[y];
    temp++;
  }
  e[Tot = 1].clear();
  int t = y;
  while (1) {
    insert((deep[y] - deep[t]) ^ a[t]);
    if (t == x) break;
    t = fa[t];
  }
  res = max(res, query(temp * 256));
  printf("%d\n", res);
}
int main() {
  scanf("%d%d", &n, &Q);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    add(x, y);
    add(y, x);
  }
  dfs(1, 0);
  for (int i = 1; i <= n; i++) {
    int u = i;
    for (int j = 1; j <= 256; j++) u = fa[u];
    g[i] = u;
    prework(i);
  }
  while (Q--) {
    int x, y;
    scanf("%d%d", &x, &y);
    solve(x, y);
  }
  return 0;
}
