v$session in procedure

[jm]

Does anyone tell me How to cursor with v$session in a procedure?

I try

CURSOR CR_SESSION IS
select sid, serial# from sys.v$session where type='USER';

or
CURSOR CR_SESSION IS
select sid, serial# from sys.v_$session where type='USER';

or
CURSOR CR_SESSION IS
select sid, serial# from v$session where type='USER';

all get error:
PLS-00201: identifier 'SYS.V$SESSION' must be declared

thanks