Here is an example of a quiz on procedures using symbolic parameters and 
overrides:

//SYMOVRID PROC SPACE='(CYL,(3,1))',SYS=a
//ST1           EXEC PGM=ONE,TIME=&TIM,
//		PARM='-9'
//DD1           DD     DSN=F1,DISP=OLD
//DD2		DD     DISP=(.PASS),UNIT=SYSDA,
//		SPACE=&SPACE
//ST2		EXEC PGM=TWO
//DD1		DD DSN=*.ST1.DD2,DISP=OLD
//DD2 	DD	SYSOUT=&SYS

Call the proc so the result will be the same as if you ran the following
job:

//MINE	JOB_______
//*
//STEP1	EXEC	PGM=A,TIME=(1,30),REGION=100K
//DD1		DD		DSN=FILE1,DISP=OLD
//DD2		DD		DSN=FILS2,UNIT=TAPE,DISP=(,PASS)
//STEP2	EXEC	PGM=TWO,REGION=90K
//DD1		DD		DSN=*.STEP1.DD2,DISP=OLD
//DD2		DD		SYSOUT=(A,,R100)
//DD3		DD		SYSOUT=*
//


Here is an answer:

//EXJ JOB 123,NET
//* CALLING SYMOVERID PROC
//ONLYST  EXEC  SYMOVRID,PGM.ST1=A,
//              TIM='(1,30)',SPACE=,
//		REGION.ST1=100K,REGION.ST2=90K,
//		SYS='(A,,R100)'
//ST1.DD1  DD  DSN=FILE1
//ST1.DD2  DD  DSN=FILE2,UNIT=TAPE
//ST2.DD3  DD  SYSOUT=*
//