#include <bits/stdc++.h>
using namespace std;
int nxt[50010 << 1], to[50010 << 1], head[50010], cnt;
void add(int u, int v) {
  nxt[++cnt] = head[u];
  to[cnt] = v;
  head[u] = cnt;
}
int f[50010][256], dep[50010], fa[50010], ffa[50010], w[50010];
void dfs(int u, int p) {
  fa[u] = p;
  dep[u] = dep[p] + 1;
  for (int i = head[u]; i; i = nxt[i]) {
    int v = to[i];
    if (v == p) continue;
    dfs(v, u);
  }
}
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) scanf("%d", &w[i]);
  for (int i = 1; i < n; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    add(u, v), add(v, u);
  }
  dfs(1, 0);
  for (int i = 1; i <= n; i++) {
    int u = i;
    for (int j = 0; j < 256 && u; j++, u = fa[u])
      f[i][(256 - 1) ^ ((w[u] ^ j) >> 8)] = max(
          f[i][(256 - 1) ^ ((w[u] ^ j) >> 8)], (w[u] ^ j) | ((256 - 1) << 8));
    ffa[i] = u;
    for (int j = 0; j < 8; j++)
      for (int k = 0; k < 256; k++)
        if (f[i][k ^ (1 << j)])
          f[i][k] = max(f[i][k], f[i][k ^ (1 << j)] ^ (1 << (j + 8)));
  }
  while (m-- > 0) {
    int u, v;
    scanf("%d%d", &u, &v);
    int ans = w[u] ^ (dep[v] - dep[u]), x = v;
    for (int i = 0; dep[u] <= dep[ffa[x]]; i++, x = ffa[x])
      ans = max(ans, f[x][i]);
    for (; dep[u] <= dep[x]; x = fa[x])
      ans = max(ans, (dep[v] - dep[x]) ^ w[x]);
    printf("%d\n", ans);
  }
  return 0;
}
