exp -> new Fac()
exp -> 10
expRests -> 
expList -> 
exp -> exp ComputeFac(expList)
statement -> System.out.println( exp ) ;
mainClass -> class Factorial{ public static void main ( String[] a) { statement } } 
varDecs -> 
type -> int
type -> int
formalRests -> 
formalList ->
varDecs -> 
type -> int
varDecs -> 
exp -> num
exp -> 1
exp -> exp < exp
exp -> 1
statement -> num_aux = exp ;
exp -> num
exp -> this
exp -> num
exp -> 1
exp -> exp - exp
expRests -> 
expList -> 
exp -> exp ComputeFac(expList)
exp -> (exp)
exp -> exp * exp
statement -> num_aux = exp ;
statement -> if ( exp ) statement else statement
statements -> 
statements ->
exp -> num_aux
methodDec -> public type ComputeFac( formalList ) { varDecs statements return exp ; }
methodDecs -> 
methodDecs -> 
classDec -> class Fac{ varDecs methodDecs }
classDecs -> 
classDecs -> classDec classDecs
program -> mainClass classDecs