Definition: Let u Î (N È T)*. G makes a
zero-step derivation from u to u; in symbols,
u Þ0 u [e] or, simply, u Þ0 u
Definition: Let u0,…,un Î (N È T)*, n ³ 1, and ui-1 Þ ui [pi], pi Î P, for all i = 1,…, n; that is
u0 Þ u1 [p1] Þ u2 [p2] … Þ un [pn]
Then, G makes n derivation steps from u0 to un,
u0 Þn un [p1... pn] or, simply, u0 Þn un 
Sequence of Derivation Steps 1/2
 Gist: Several consecutive derivation steps.
6/50