In: Information Processing Letters 41. 1992.
Abstract: We add an extension called debit arcs to traditional place/transition nets. A debit arc incident upon a transition represents an always true precondition: when the transition fires, a token is subtracted from the place issuing the debit arc, creating an antitoken if no tokens are present to subtract. We show that two different policies on how tokens and antitokens annihilate produce two classes of automata with different recognition powers.