#include<bits/stdc++.h>
using namespace std;
#define rep(i,x,y) for (int i=(x);i<=(y);i++)
#define drep(i,y,x) for (int i=(y);i>=(x);i--)
#define pii pair<int,int>
#define fir first
#define sec second
#define MP make_pair
template<typename T> bool chkmin(T &x,T y){return x>y?x=y,1:0;}
template<typename T> bool chkmax(T &x,T y){return x<y?x=y,1:0;}
void file() {
    #ifdef zqj
    freopen("a.in","r",stdin);
    #endif
}
typedef long long ll;
#define sz 2333

int n,m,A,B;
vector<int>V[sz];
set<pii>E;
int w[sz],_w[sz];

vector<int>G[sz];
namespace bipolar_orientation {
    int dfn[sz],low[sz],cc,p[sz],inv[sz],topo[sz];
    bool flg,sgn[sz];
    void dfs(int x,int fa,int s,int t) {
        dfn[x]=low[x]=++cc; inv[cc]=x,p[x]=fa;
        if (x==s) dfs(t,x,s,t);
        for (int y:G[x]) {
            if (x==s&&y==t) continue;
            if (!dfn[y]) {
                dfs(y,x,s,t);
                chkmin(low[x],low[y]);
                if (x==s||low[y]>=dfn[x]) flg=1;
            }
            else if (dfn[y]<dfn[x]&&y!=fa) chkmin(low[x],dfn[y]);
        }
    }
    int check(int s,int t,int n) {
        if (n==1) return topo[1]=1,1;
        if (s==t) return 0;
        cc=flg=0; dfs(s,s,s,t);
        if (flg) return 0;
        sgn[s]=0;
        static int pre[sz],suf[sz];
        suf[0]=s,pre[s]=0,suf[s]=t;
        pre[t]=s,suf[t]=n+1,pre[n+1]=t;
        rep(i,3,n) {
            int v=inv[i];
            if (!sgn[inv[low[v]]]) {
                int P=pre[p[v]];
                pre[v]=P,suf[v]=p[v];
                suf[P]=pre[p[v]]=v;
            }
            else {
                int S=suf[p[v]];
                pre[v]=p[v],suf[v]=S;
                suf[p[v]]=pre[S]=v;
            }
            sgn[p[v]]=!sgn[inv[low[v]]];
        }
        for (int x=s,cnt=0;x!=n+1;x=suf[x]) topo[++cnt]=x;
        return 1;
    }
    void clr(int n) {
        rep(i,1,n) dfn[i]=low[i]=p[i]=inv[i]=topo[i]=sgn[i]=0,G[i].clear();
    }
}

vector<int>path;
void dfs(int x,int ww) {
    path.push_back(x);
    int mn=1e9,vv=-1;
    for (auto v:V[x]) if (chkmin(mn,w[v])) vv=v;
    if (mn>ww) return;
    swap(w[x],w[vv]);
    dfs(vv,ww);
}

int main(){
    file();
    ios::sync_with_stdio(0),cin.tie(0);
    cin>>n>>m>>A>>B;
    rep(i,1,n) cin>>w[i],_w[i]=w[i];
    int x,y;
    while (m--) cin>>x>>y,G[x].push_back(y),G[y].push_back(x),E.insert(minmax(x,y));
    if (!bipolar_orientation::check(A,B,n)) return puts("-1"),0;
    using bipolar_orientation::topo;
    static int rnk[sz],pre[sz],suf[sz];
    rep(i,1,n) rnk[topo[i]]=i;
    rep(x,1,n) for (auto v:G[x]) if (rnk[v]>rnk[x]) V[x].push_back(v),pre[v]=x,suf[x]=v;
    rep(i,1,n) if ((i!=A&&!pre[i])||(i!=B&&!suf[i])) assert(0);
    vector<vector<int>>ans;
    drep(r,n-1,1) {
        path.clear();
        int ww=w[A],x=topo[r];
        dfs(x,ww);
        swap(ww,w[path.back()]);
        vector<int>p2;
        for (int xx=pre[x];xx;xx=pre[xx]) swap(ww,w[xx]),p2.push_back(xx);
        reverse(p2.begin(),p2.end());
        ans.push_back(p2);
        for (auto t:path) ans.back().push_back(t);
    }
    rep(i,1,n) for (auto v:V[i]) assert(w[i]<w[v]);
    cout<<ans.size()<<'\n';
    for (auto p:ans) {
        cout<<p.size()<<' ';
        for (auto x:p) cout<<x<<' ';
        cout<<'\n';
        assert((int)p.size());
        rep(i,0,(int)p.size()-2) assert(E.count(minmax(p[i],p[i+1]))),swap(_w[p[i]],_w[p[i+1]]);
        assert(p[0]==A);
        sort(p.begin(),p.end()),assert(unique(p.begin(),p.end())==p.end());
    }
    rep(i,1,n) for (auto v:V[i]) assert(_w[i]<_w[v]);
    assert(topo[1]==A&&topo[n]==B);
    return 0;
}