Inputs: {'type': 'PortionOfFluid', 'count': 1, 'constraints': 'at least one of the three ports functions as an inlet'}

Outputs: {'type': 'PortionOfFluid', 'count': 2, 'constraints': 'the remaining two ports function as outlets in diverting service (one inlet routed to one of two outlets); in mixing service the roles invert -- two ports serve as inlets converging into one outlet'}

Transformation: fluid routed among three ports, either splitting one inlet stream into two outlets (diverting) or merging two inlet streams into one outlet (mixing), depending on plumbing and service