States Can Sometimes Do More Than Stack Symbols in PDA's. - John K. Price; Detlef Wotschke (ICALP, 1978)

On Reducing the Number of States in a PDA. - Jonathan Goldstine; John K. Price; Detlef Wotschke (Math. Syst. Theory, 1982)

A Pushdown Automaton or a Context-Free Grammar - Which is More Economical? - Jonathan Goldstine; John K. Price; Detlef Wotschke (Theor. Comput. Sci., 1982)

On Reducing the Number of Stack Symbols in a PDA. - Jonathan Goldstine; John K. Price; Detlef Wotschke (Math. Syst. Theory, 1993)