transit build transit object own state object sourc object dest own state composit state illeg argument except own state sourc state vertex illeg argument except sourc dest state vertex illeg argument except dest composit state composit state composit state own state composit state subvertex contain sourc composit state subvertex contain dest transit tran creat transit composit state intern transit add tran tran set sourc state vertex sourc tran set target state vertex dest tran illeg argument except build transit argument legal 