1. understood that symbol string and set operations.
L={A,B, … ,Z,a,b, … ,z}
D={0,1, … ,9}
Description meaning under represented:
LUD: a collection of all the numbers and letters
LD: the set of all symbols consisting of a letter followed by a number composed of
L4: 4 by a set of letters
L *: all the alphabet symbol string set
D +: the set of all strings of symbols by one or several digits
L (LUD) *: the set of all strings of symbols with the letter, followed by letters, digits
2. grammar G (Z): Z-> aZb | ab definition of what kind of language?
Because: z-> aZb | ab
所以：Z->aZb->aaZbb->aaaZbbb->an bn
3. Write materials 22 is this page embodiment 2.2 grammar in the form of four-tuple identifier (the VN, NT, P, S) .
I->I | IL |ID
L->a|b|c|...|x|y|z
D->0|1|...|8|9
4. Write the following expressions leftmost derivation, rightmost derivation.
G (E):
E=> E + T | T
T=>T * F | F
F=>（E）| i
i*i+i
i+i*i
i+(i+i)
Observe different leftmost and rightmost derivation process.
Most right:
[i*i+i] E=>E+T=>E+F=>E+i=>T+i=>T*F+i=>T*i+i=>F*i+i=>i*i+i
[i+i*i] E=>E+T=>E+T*F=>E+T*i=>E+F*i=>E+i*i=>T+i*i=>F+i*i=>i+i*i
[i+(i+i)] E=>E+T=>E+F=>E+(E)=>E+(E+T)=>E+(E+F)=>E+(E+i)=>E+(T+i)=>E+(F+i)=>E+(i+i)=>T+(i+i)=>F+(i+i)=>i+(i+i)
leftmost:
[i*i+i] E=>E+T=>T+T=>T*F+T=>F*F+T=>i*F+T=>i*i+T=>i*i+F=>i*i+i
[i+i*i] E=>E+T=>T+T=>F+T=>i+T=>i+T*F=>i+F*F=>i+i*F=>i+i*i
[i+(i+i)] E=>E+T=>T+T=>F+T=>i+T=>i+F=>i+(E)=>i+(E+T)=>i+(T+T)=>i+(F+T)=>i+(i+T)=>i+(i+F)=>i+(i+i)