Empty(X1X2…Xn): Example
27/57
Empty(E) :=  Æ
Empty(E’) := {e}
Empty(T) :=  Æ
Empty(T’) := {e}
Empty(F) :=  Æ
Gexpr3 = (N, T, P, E), where: N = {E, F, T}, T = {i, +, *, (, )},
P = { 1: E  ® TE’,   2: E’ ® +TE’, 3: E’ ® e,    4: T  ® FT’
5: T’ ® *FT’, 6: T’ ® e,        7: F  ® (E), 8: F  ® i }
Set Empty
for all X Î N:
Task: Empty(E’T’)
Empty(E’) = Empty(T’) = {e}, so Empty(E’T’) = {e}