diff -urN wf-/data.c wf/data.c
--- wf-/data.c	Mon Jan  4 00:00:00 2016
+++ wf/data.c	Wed Jan  6 00:00:00 2016
@@ -18,6 +18,7 @@
 	CASE_RET(type_circle);
 	CASE_RET(type_ball);
 	CASE_RET(type_arc);
+	CASE_RET(type_octahedron);
 	CASE_RET(type_arr);
 	CASE_RET(type_op_data_set);
 	CASE_RET(type_slice);
@@ -33,6 +34,9 @@
 	CASE_RET(type_slide_way);
 	CASE_RET(type_slide_way_liss);
 	CASE_RET(type_rot_way);
+	CASE_RET(type_rdiv_way);
+	CASE_RET(type_rail_way);
+	CASE_RET(type_train_way);
 	CASE_RET(type_copy);
 	CASE_RET(type_copy_rot);
 	CASE_RET(type_copy_point_symmetry);
@@ -228,8 +232,8 @@
 				{-1,-1,-1},{1,-1,-1},{1,1,-1},{-1,1,-1},
 				{-1,-1,1},{1,-1,1},{1,1,1},{-1,1,1} },
 			(int[]){
-				0,1,2,3,0,-1, 4,5,6,7,4,-1,
-				0,4,-1, 1,5,-1, 2,6,-1, 3,7,-1, -1 }, wk, &wk[8] }
+				0,1,2,3,0,4,5,6,7,4,-1,
+				1,5,-1, 2,6,-1, 3,7,-1, -1 }, wk, &wk[8] }
 	};
 	data_draw(&data, prm);
 }
@@ -301,6 +305,21 @@
 }
 
 static void
+octahedron_draw(prm_t *prm)
+{
+	d3_t wk[6*2];
+	data_t data = {
+		type_wire_frame,
+		&(struct wire_frame){
+			6,
+			(pos_t[]){ {0,0,1},{1,0,0},{0,1,0},{-1,0,0},{0,-1,0},{0,0,-1} },
+			(int[]){ 0,1,5,3,0,2,5,4,0,-1, 1,2,3,4,1,-1, -1 },
+			wk, &wk[6] }
+	};
+	data_draw(&data, prm);
+}
+
+static void
 arr_draw(data_t *data, prm_t *prm)
 {
 	for(; data->type!=type_end; data++){
@@ -362,6 +381,9 @@
 	case type_arc:
 		arc_draw(data->p, prm);
 		break;
+	case type_octahedron:
+		octahedron_draw(prm);
+		break;
 
 	case type_arr:
 		arr_draw(data->p, prm);
@@ -531,6 +553,41 @@
 }
 
 static void
+op_data_rail_way(struct rail_way *rlw, data_t *data, prm_t *prm)
+{
+	struct way way = rlw->way;
+	pos_t p_f, p_r;
+	vec_t vy;
+	axis_t ax;
+	affin_t af;
+
+	way_get_back_t(&way, prm->sec, rlw->len, &p_r);
+	p_f = way.ret_p;
+
+	vec_set(&vy, &p_r, &p_f);
+	axis_set(&ax, &p_f, &vy);
+
+	affin_axis_rconv(&af, &ax);
+	affin_compo(&prm->af, &prm->af, &af);
+	data_draw(data, prm);
+}
+
+static void
+op_data_train_way(struct train_way *tw, data_t *data, prm_t *prm)
+{
+	struct way way = tw->way;
+	struct rail_way rlw = { .len = tw->len, .way = tw->way };
+	data_t op = { type_rail_way, &rlw };
+	int i;
+
+	for(i=0; i<tw->n; i++){
+		op_data_draw(&op, data, prm);
+		prm->sec = way_get_back_t(&way, prm->sec, tw->len, NULL);
+		prm->sec = way_get_back_t(&way, prm->sec, tw->len2, NULL);
+	}
+}
+
+static void
 op_data_copy(struct copy *copy, data_t *data, prm_t *prm)
 {
 	int x, y, z;
@@ -663,6 +720,12 @@
 		break;
 	case type_rdiv_way:
 		op_data_rdiv_way(op->p, data, prm);
+		break;
+	case type_rail_way:
+		op_data_rail_way(op->p, data, prm);
+		break;
+	case type_train_way:
+		op_data_train_way(op->p, data, prm);
 		break;
 
 	case type_copy:
diff -urN wf-/data.h wf/data.h
--- wf-/data.h	Mon Jan  4 00:00:00 2016
+++ wf/data.h	Wed Jan  6 00:00:00 2016
@@ -20,6 +20,7 @@
 #define type_circle			5
 #define type_ball			6
 #define type_arc			7
+#define type_octahedron			8
 
 #define type_arr			10
 #define type_op_data_set		11
@@ -39,6 +40,8 @@
 #define type_slide_way_liss		121
 #define type_rot_way			130
 #define type_rdiv_way			131
+#define type_rail_way			132
+#define type_train_way			133
 
 #define type_copy			200
 #define type_copy_rot			201
@@ -122,6 +125,17 @@
 struct rdiv_way{
 	int n;
 	struct way rate_way;
+};
+
+struct rail_way{
+	double len;
+	struct way way;
+};
+
+struct train_way{
+	int n;
+	double len, len2;
+	struct way way;
 };
 
 struct copy{
diff -urN wf-/way.c wf/way.c
--- wf-/way.c	Sun Jan  3 02:00:00 2016
+++ wf/way.c	Wed Jan  6 00:00:00 2016
@@ -103,6 +103,47 @@
 	}
 }
 
+double
+way_get_back_t(struct way *way, double t, double len, pos_t *ret_back_pos)
+{
+	int n = way->n, idx, nxt;
+	double tmp = t, spd, back_sec, l, r;
+	struct way w;
+
+	if(!way->ps) ERR("way->ps NULL");
+
+	way_get(way, t);
+	w = *way;
+
+	idx = way_idx_rate(way->ts, n, &tmp);
+	do{
+		while(way->ts[idx] <= 0) idx = (idx - 1 + n) % n;
+		nxt = (idx + 1) % n;
+		spd = pos_distance(&way->ps[idx], &way->ps[nxt]) / way->ts[idx];
+		idx = nxt;
+	}while(spd == 0);
+	
+	tmp = t;
+	back_sec = len / spd;
+	do{
+		tmp -= back_sec;
+		way_get(way, tmp);
+	}while(pos_distance(&w.ret_p, &way->ret_p) < len);
+
+	l = tmp;
+	r = t;
+	while(r - l > 0.000001){
+		tmp = (l + r) * 0.5;
+		way_get(way, tmp);
+		if(pos_distance(&w.ret_p, &way->ret_p) > len) l = tmp;
+		else r = tmp;
+	}
+
+	if(ret_back_pos) *ret_back_pos = way->ret_p;
+	*way = w;
+	return tmp;
+}
+
 void
 way_liss_init(struct way_liss *wl, const pos_t *ps, const pos_t *pe, const d3_t *sec, const d3_t *init_sec)
 {
diff -urN wf-/way.h wf/way.h
--- wf-/way.h	Sun Jan  3 02:00:00 2016
+++ wf/way.h	Wed Jan  6 00:00:00 2016
@@ -34,6 +34,7 @@
 
 int way_idx_rate(const double *ts, int n, double *t);
 void way_get(struct way *way, double t);
+double way_get_back_t(struct way *way, double t, double len, pos_t *ret_back_pos);
 
 
 struct way_liss{
diff -urN wf-/wf_ex.c wf/wf_ex.c
--- wf-/wf_ex.c	Mon Jan  4 00:00:00 2016
+++ wf/wf_ex.c	Wed Jan  6 00:00:00 2016
@@ -366,7 +366,7 @@
 		data_t *fireworks = &(data_t){ type_op_data_set, &(struct op_data_set){
 		    .op = &(data_t){ type_arr, (data_t[]){
 			{ type_copy_timeshift_rot, &(struct copy_timeshift_rot){
-			    .n=6, .init_sec=0, .step_sec=2, .l=LINE_Z, .init_deg=0, .step_deg=360/6 }},
+			    .n=3, .init_sec=0, .step_sec=2, .l=LINE_Z, .init_deg=0, .step_deg=360/3 }},
 			{ type_copy_timeshift, &(struct copy_timeshift){
 			    .n=3, .init_sec=0, .step_sec=-1, .init={200,0,0}, .step=D3_O }},
 			{ type_slide_way, &(struct way){
@@ -384,6 +384,25 @@
 			{ type_end } }},
 		    .data = spin_ball }};
 
+		double a = 10, b = a*2;
+		struct way *rail = &(struct way){
+		  .n=20, 
+		  .ps = (pos_t[]){
+		    {a,0,0},{a+b,0,0},{a+b+b,a,0},{a+b+b+b,a,0},{a+b+b+b+a,a+a,0},{a+b+b+b,a+a+a,0},
+		    {a+b+b,a+a+a,0},{a+b,a+a+a,a},{a,a+a+a,a},{0,a+a,a},{a,a,a},
+		    {a+b,a,a},{a+b+b,0,a},{a+b+b+b,0,a},{a+b+b+b+a,a,a},{a+b+b+b,a+a,a},
+		    {a+b+b,a+a,a},{a+b,a+a,0},{a,a+a,0},{0,a,0} },
+		  .ts=(double[]){ 3,4,3,1,1, 1,2,1,0.5,0.5, 3,4,3,1,1, 1,2,1,0.5,0.5 },
+		  .vs=NULL, .dg=3 };
+
+		data_t *train = &(data_t){ type_op_data_set, &(struct op_data_set){
+		  .op = &(data_t){ type_arr, (data_t[]){
+		    { type_slide, &(d3_t){0,-4*a,0} },
+		    { type_train_way, &(struct train_way){.n=6, .len=4, .len2=4, .way=*rail} },
+		    { type_zoom_and_slide, (d3_t[]){ {1,4,1},{0,-2,0} } },
+		    { type_end } }},
+		  .data = &(data_t){ type_cube } }};
+
 		data.type = type_arr;
 		data.p = (data_t[]){
 			*axyz,
@@ -393,6 +412,7 @@
 			*exile, *lissajours,
 			*half_pipe,
 			*fireworks,
+			*train,
 			{ type_end }
 		};
 	}