#include<cstdio>
#include<vector>
#include<queue>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<ctime>
#include<random>
#include<array>
#include<assert.h>
#define pb emplace_back
#define mp make_pair
#define fi first
#define se second
#define dbg(x) cerr<<"In Line "<< __LINE__<<" the "<<#x<<" = "<<x<<'\n'
#define dpi(x,y) cerr<<"In Line "<<__LINE__<<" the "<<#x<<" = "<<x<<" ; "<<"the "<<#y<<" = "<<y<<'\n'
#define DE(fmt,...) fprintf(stderr, "Line %d : " fmt "\n",__LINE__,##__VA_ARGS__)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int>pii;
typedef pair<ll,int>pli;
typedef pair<ll,ll>pll;
typedef pair<int,ll>pil;
typedef vector<int>vi;
typedef vector<ll>vll;
typedef vector<pii>vpii;
typedef vector<pll>vpll;
template<typename T>T cmax(T &x, T y){return x=x>y?x:y;}
template<typename T>T cmin(T &x, T y){return x=x<y?x:y;}
template<typename T>
T &read(T &r){
	r=0;bool w=0;char ch=getchar();
	while(ch<'0'||ch>'9')w=ch=='-'?1:0,ch=getchar();
	while(ch>='0'&&ch<='9')r=r*10+(ch^48),ch=getchar();
	return r=w?-r:r;
}
template<typename T1,typename... T2>
void read(T1 &x,T2& ...y){read(x);read(y...);}
const int N=1010;
int n,m,s,t;
vi eg[N],L[N];
int fa[N],dfn[N],low[N],rk[N],ot[N],dft,cut;
void dfs(int x){
	dfn[x]=low[x]=++dft;rk[dft]=x;
	for(auto v:eg[x])if(v!=fa[x]){
		if(!dfn[v]){
			fa[v]=x;ot[x]++;
			dfs(v);
			cmin(low[x],low[v]);
			if(low[v]>=dfn[x]&&x!=s)cut=1;
		}
		else cmin(low[x],dfn[v]);
	}
	if(x==s&&ot[x]>=2)cut=1;
}
int col[N],cct,pos[N];
void ins(int x){
	col[x]=++cct;pos[cct]=x;
	for(auto v:L[x])if(!col[v])ins(v);
}
int a[N],fr[N];
vi E[N];
signed main(){
	read(n,m,s,t);
	for(int i=1;i<=n;i++)read(a[i]);
	for(int i=1;i<=m;i++){
		int u,v;read(u,v);
		eg[u].pb(v);eg[v].pb(u);
	}
	eg[s].pb(t);eg[t].pb(s);
	dfs(s);
	if(cut){puts("-1");return 0;}
	eg[s].pop_back();eg[t].pop_back();
	dft=0;for(int i=1;i<=n;i++)dfn[i]=low[i]=fa[i]=ot[i]=0;
	dfs(s);
	queue<int>q;
	for(int i=1;i<=n;i++)if(!ot[i])q.push(i);
	while(!q.empty()){
		int x=q.front();q.pop();
		if(x==t)continue;
		L[fa[x]].pb(x);L[rk[low[x]]].pb(x);
		if(!--ot[fa[x]])q.push(fa[x]);
	}
	vi go;
	for(int x=t;x;x=fa[x])go.pb(x);
	reverse(go.begin(),go.end());
	for(auto i:go)ins(i);
//	for(int i=1;i<=n;i++)dbg(pos[i]);
	for(int i=1;i<=n;i++)
		for(auto j:eg[i])
			if(col[i]<col[j]){
				E[i].pb(j);
				fr[j]=i;
			}
	vector<vi>outp;
	for(int i=n-1;i>=1;i--){
		int x=pos[i];
		int fl=1;
		for(auto v:E[x])if(a[v]<a[x])fl=0;
		if(fl)continue;
		vi vec;
		while(x){
			vec.pb(x);x=fr[x];
		}
		reverse(vec.begin(),vec.end());
		x=pos[i];
		while(1){
			int v=-1;
			for(auto i:E[x])if(v==-1||a[i]<a[v])v=i;
			if(v==-1||a[v]>a[s])break;
			x=v;vec.pb(x);
		}
		outp.pb(vec);
		int len=vec.size();
		int c=a[vec[0]];
		for(int i=0;i+1<len;i++)a[vec[i]]=a[vec[i+1]];
		a[vec[len-1]]=c;
	}
	cout<<outp.size()<<'\n';
	for(auto &w:outp){
		cout<<w.size()<<' ';
		for(auto i:w){
			cout<<i<<' ';
		}
		puts("");
	}
    #ifdef do_while_true
//		cerr<<'\n'<<"Time:"<<1.0*clock()/CLOCKS_PER_SEC*1000<<" ms"<<'\n';
	#endif
	return 0;
}