#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef vector<long long> vll;
typedef pair<int,int> pint;
typedef pair<long long, long long> pll;

#define MP make_pair
#define PB push_back
#define ALL(s) (s).begin(),(s).end()
#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P) 
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P) 
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P) 
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s; }
inline long long tonum(string s) {long long v;istringstream sin(s);sin>>v;return v;}
template<class T> inline string tostr(T x) {ostringstream sout;sout<<x;return sout.str();}



template<class T> struct Edge {
    int from, to;
    T cost;
    Edge(int f, int t, T c) : from(f), to(t), cost(c) {}
    friend bool operator < (const Edge &e1, const Edge &e2) {return e1.cost < e2.cost;}
    friend bool operator > (const Edge &e1, const Edge &e2) {return e1.cost > e2.cost;}
    friend ostream& operator << (ostream& s, const Edge<T>& E) {
        return s << E.from << "->" << E.to << '(' << E.cost << ')';
    }
};

const int MAX_V = 300;
template<class T> struct Graph {
    int V;
    vector<Edge<T> > list[MAX_V];
    
    Graph(int n = 0) : V(n) {}
    void init(int n = 0) {V = n; for (int i = 0; i < MAX_V; ++i) list[i].clear();}
    void resize(int n = 0) {V = n;}
    inline vector<Edge<T> >& operator [] (int i) {return list[i];}
    
    void direct(int f, int t, T c) {
        list[f].push_back(Edge<T>(f,t,c));
        list[t].push_back(Edge<T>(t,f,-c));
    }
    
    friend ostream& operator << (ostream& s, const Graph& G) {
        s << endl; for (int i = 0; i < G.V; ++i) {s << i << " : " << G.list[i] << endl;}return s;
    }
};

Graph<int> G;



int n;
string str;

bool ok = true;
bool seen[MAX_V];
int dist[MAX_V];
void rec(int v) {
    seen[v] = true;
    
    //cout << v << " : " << dist[v] << endl;
    
    vint next;
    for (int i = 0; i < G[v].size(); ++i) {
        int to = G[v][i].to, c = G[v][i].cost;
        
        if (!seen[to]) {
            dist[to] = dist[v] + c;
            next.push_back(to);
        }
        else if ( dist[to] != dist[v] + c) ok = false;
    }
    for (int i = 0; i < next.size(); ++i) rec(next[i]);
}

int main() {
    //freopen( "/Users/macuser/Dropbox/Contest/input.in", "r", stdin );
    while (scanf("%d\n", &n) != EOF) {
        if (n == 0) break;
        G.init(110);
        
        map<string,int> ma;
        int it = 0;
        for (int i = 0; i < n; ++i) {
            getline(cin, str);
            
            istringstream sin(str);
            string pre, s1, equ, ratio, s2;
            sin >> pre >> s1 >> equ >> ratio >> s2;
            
            //cout << pre << ", " << s1 << ", " << equ << ", " << ratio << ", " << s2 << endl;
            
            ratio = ratio.substr(3);
            int num = tonum(ratio);
            
            //COUT(num);
            
            if (!ma.count(s1)) ma[s1] = it++;
            if (!ma.count(s2)) ma[s2] = it++;
            
            G.direct(ma[s1], ma[s2], num);
        }
        G.resize(it);
        
        //COUT(G);

        ok = true;
        memset(seen, 0, sizeof(seen));
        memset(dist, -1, sizeof(dist));
        for (int i = 0; i < it; ++i) {
            if (!seen[i]) {
                dist[i] = 0;
                rec(i);
            }
        }
        if (ok) puts("Yes");
        else puts("No");
    }
    return 0;
}


Measured memory_bytes: 1336