Singleton offers client-preferred payment methods to replace service providers' original payment methods.
When you enters Europe, even for public transport on the land, it is so hard to find a uniform way to buy the ticket and order the service. Along a journey, Singleton provide contract libraries to help traditional service provider generally define their tokens compatible with their original payment methods. Those contracts are like Legos, intermediate service providers could flexibly provide integral mobile solutions combing different original service providers without negotiating with them.
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