#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>#include <queue>const double eps = 1e-10;using namespace std;struct point{double x, y;point( double _x = 0., double _y = 0. ) : x(_x), y(_y) {}point nor(){double L = sqrt(x*x+y*y);return point(x/L, y/L);}} L[200][2], p[1000];int dcmp( double x ){if( x < -eps )return -1;return x > eps;}double cross( point k, point a, point b ){return (a.x-k.x)*(b.y-k.y) - (a.y-k.y)*(b.x-k.x);}double dot( point k, point a, point b ){return (a.x-k.x)*(b.x-k.x) + (a.y-k.y)*(b.y-k.y);}bool segCross( point a, point b, point c, point d ){int d1, d2, d3, d4;d1 = dcmp(cross(a, b, c));d2 = dcmp(cross(a, b, d));d3 = dcmp(cross(c, d, a));d4 = dcmp(cross(c, d, b));if( (d1^d2) == -2 && (d3^d4) == -2 )return 1;return 0;}queue<int> Q;bool vis[1000];bool bfs( int S, int T, int np, int nl ){memset(vis, 0, sizeof(vis));vis[S] = 1;Q.push(S);while( !Q.empty() ){int u = Q.front();Q.pop();for( int i = 0; i < np; ++i )if( !vis[i] ){bool ok = 1;for( int j = 0; ok && j < nl; ++j )if( segCross(p[u], p[i], L[j][0], L[j][1]) )ok = 0;if( ok ){vis[i] = 1;Q.push(i);}}}return vis[T];}bool chk( point p, int nl ){for( int i = 0; i < nl; ++i )if( dcmp(cross(p, L[i][0], L[i][1])) == 0 && dcmp(dot(p, L[i][0], L[i][1])) < 0 )return 0;return 1;}int main(){int N, e;double d = 0.00001;while( scanf("%d", &N), N ){e = 0;p[e++] = point(0., 0.);p[e++] = point(1000., 1000.);for( int i = 0; i < N; ++i ){scanf("%lf %lf %lf %lf", &L[i][0].x, &L[i][0].y, &L[i][1].x, &L[i][1].y);point v = point(L[i][1].x-L[i][0].x, L[i][1].y-L[i][0].y).nor();L[i][0] = point(L[i][0].x - v.x*d, L[i][0].y - v.y*d);L[i][1] = point(L[i][1].x + v.x*d, L[i][1].y + v.y*d);}for( int i = 0; i < N; ++i ){if( chk(L[i][0], N) )p[e++] = L[i][0]; if( chk(L[i][1], N) )p[e++] = L[i][1];}if( bfs(0, 1, e, N) )puts("no");elseputs("yes");}return 0;}
