-let t1 = (make_list 1 empty) in
-let t2 = (make_list 2 empty) in
-let t3 = (make_list 3 empty) in
-let t12 = (make_list t1 (make_list t2 empty)) in
-let t23 = (make_list t2 (make_list t3 empty)) in
-let ta = (make_list t1 t23) in
-let tb = (make_list t12 t3) in
-let tc = (make_list t1 (make_list t23 empty)) in
+let t1 = (make\_list 1 empty) in
+let t2 = (make\_list 2 empty) in
+let t3 = (make\_list 3 empty) in
+let t12 = (make\_list t1 (make\_list t2 empty)) in
+let t23 = (make\_list t2 (make\_list t3 empty)) in
+let ta = (make\_list t1 t23) in
+let tb = (make\_list t12 (make\_list t3 empty)) in
+let tc = (make\_list t1 (make\_list t23 empty)) in