Definition:
Let
xApay and xwqy be two configurations of a PDA, M, where
x, w Î G*, A Î G, p, q Î Q, a Î S È {e}, and y Î S*.
Let r = Apa ® wq Î R be a rule. Then, M makes
a move from xApay to xwqy
according to r, written as
xApay |– xwqy [r] or,
simply,
xApay |– xwqy.