#include<bits/stdc++.h>

#define ll long long
#define mk make_pair
#define fi first
#define se second

using namespace std;

inline int read(){
	int x=0,f=1;char c=getchar();
	for(;(c<'0'||c>'9');c=getchar()){if(c=='-')f=-1;}
	for(;(c>='0'&&c<='9');c=getchar())x=x*10+(c&15);
	return x*f;
}

const int mod=998244353;
int ksm(int x,ll y,int p=mod){
	int ans=1;y%=(p-1);
	for(int i=y;i;i>>=1,x=1ll*x*x%p)if(i&1)ans=1ll*ans*x%p;
	return ans%p;
}
int inv(int x,int p=mod){return ksm(x,p-2,p)%p;}
mt19937 rnd(time(0));
int randint(int l,int r){return rnd()%(r-l+1)+l;}
void add(int &x,int v){x+=v;if(x>=mod)x-=mod;}
void Mod(int &x){if(x>=mod)x-=mod;}
int cmod(int x){if(x>=mod)x-=mod;return x;}

template<typename T>void cmax(T &x,T v){x=max(x,v);}
template<typename T>void cmin(T &x,T v){x=min(x,v);}

const int N=1005;

int n,m,a[N],order[N],A,B,rk[N];
vector<pair<int,int> >edges;

namespace Bipolar{

vector<int>G[N];
int dfn[N],low[N],fa[N],son[N],ocnt,dfc=0,anc[N];

void adde(int u,int v){
	G[u].emplace_back(v),G[v].emplace_back(u);
}

bool cut=0;
void dfs(int u){
	anc[u]=u,dfn[u]=++dfc,low[u]=dfn[u];
//	cout<<"dfs "<<u<<" dfn = "<<dfn[u]<<endl;
	for(int v:G[u]){
		if(!dfn[v]){
//			cout<<" "<<u<<" -> son = "<<v<<endl;
			fa[v]=u,dfs(v),cmin(low[u],low[v]),son[u]++;
//			cout<<" low "<<v<<" = "<<low[v]<<" dfn = "<<dfn[u]<<endl;
			if(low[v]>=dfn[u])cut=true;
		}
		else{
			if(dfn[v]<dfn[anc[u]])anc[u]=v,
			cmin(low[u],dfn[v]);
		}
	}
}
vector<int>nxt[N];
bool vis[N];
void ins(int u){
	order[++ocnt]=u,vis[u]=1;
	for(int v:nxt[u])if(!vis[v])ins(v);
}
bool Solve(int s,int t){
	adde(s,t);
	
	dfs(s);
	if(son[s]>=2||cut)return false;
	
	G[s].erase(--G[s].end()),G[t].erase(--G[t].end());
	memset(dfn,0,sizeof(dfn)),memset(low,0,sizeof(low)),dfc=0;
	dfs(s);
	
	queue<int>q;
	for(int i=1;i<=n;i++)if(son[i]==0)q.push(i);
	while(q.size()){
		int x=q.front();q.pop();if(x==t)continue;
		nxt[fa[x]].emplace_back(x),nxt[anc[x]].emplace_back(x);
		if(--son[fa[x]]==0)q.push(fa[x]);
	}
	
	vector<int>nodes;
	int x=t;nodes.emplace_back(t);
	while(x!=s)x=fa[x],nodes.emplace_back(x);
	reverse(nodes.begin(),nodes.end());
	
	for(int x:nodes)ins(x);
	
	return true;
}

}

vector<int>G[N];
int fa[N];

signed main(void){

#ifndef ONLINE_JUDGE
	freopen("in.in","r",stdin);
//	freopen("out.out","w",stdout);
#endif

	n=read(),m=read(),A=read(),B=read();edges.resize(m);
	for(int i=1;i<=n;i++)a[i]=read();
	for(int i=0;i<m;i++)edges[i].fi=read(),edges[i].se=read();
	
	for(auto [u,v]:edges)Bipolar::adde(u,v);
	if(!Bipolar::Solve(A,B))return puts("-1"),0;
	
//	cout<<"order = ";for(int i=1;i<=n;i++)cout<<order[i]<<" ";puts("");
	
	for(int i=1;i<=n;i++)rk[order[i]]=i;
	for(auto [u,v]:edges){
		if(rk[u]>rk[v])swap(u,v);
		G[u].emplace_back(v),fa[v]=u;
	}
	
	vector<vector<int> >ans;
	for(int i=n-1;i>=1;i--){
		int x=order[i];bool chk=0;
		for(int y:G[x])if(a[y]<a[x])chk=1;
		if(!chk)continue;
		
//		cout<<"x = "<<x<<endl;
		
		vector<int>nodes(1,x);
		while(x!=A)x=fa[x],nodes.emplace_back(x);
		reverse(nodes.begin(),nodes.end());
		
//		cout<<"now nodes = ";for(int x:nodes)cout<<x<<" ";puts("");
		
		x=order[i];
		while(x!=B){
			int p=-1;
			for(int y:G[x])if(p==-1||a[y]<a[p])p=y;
			if(p==-1||a[p]>a[A])break;
			nodes.emplace_back(p),x=p;
		}
		
		ans.emplace_back(nodes);
		int cur=a[A];
		for(int i=0;i+1<nodes.size();i++)a[nodes[i]]=a[nodes[i+1]];
		a[nodes.back()]=cur;
	}
	
	cout<<ans.size()<<endl;
	for(auto op:ans){
		cout<<op.size()<<" ";
		for(int x:op)cout<<x<<" ";puts("");
	}

	return 0;
}