Abstraction and empty process in process algebra

Formulates a system ACPc, which is a conservative extension of the systems ACP/sub eta /, ACP square root , but also of ACP/sub tau /. This is a general system, in which most relevant issues can be discussed. Abstraction from internal steps can be achieved in two ways, in two stages: one can abstract to the hidden step eta , and then from eta to Milner's silent step ta