Given the following statements: S1: A foreign key declaration can always be…

Given the following statements:

S1: A foreign key declaration can always be replaced by an equivalent check  assertion in SQL. 

S2: Given the table $R(a,b,c)$ where $a$ and $b$ together form the primary key, the following is a valid table definition.

CREATE TABLE S (
    a INTEGER,
    d INTEGER,
    e INTEGER,
    PRIMARY KEY (d),
    FOREIGN KEY (a) references R)

Which one of the following statements is CORRECT?