[PL/SQL] Differenza tra IS e AS?

[Matrixbob]

Dalla guida "automi a stati finiti" online non specifica la differenza:
Procedure Declaration and Definition

Inoltre ho trovato un esempio simile:

CREATE PROCEDURE remove_emp (employee_id NUMBER) AS
tot_emps NUMBER;
BEGIN
DELETE FROM employees
WHERE employees.employee_id = remove_emp.employee_id;
tot_emps := tot_emps - 1;
END;

CREATE PROCEDURE find_root
( x IN REAL )
IS LANGUAGE C
NAME c_find_root
LIBRARY c_utils
PARAMETERS ( x BY REFERENCE );