redundancy in CHECK CONSTRAINTs

I have the following table:

CREATE TABLE gyuktnine (
id SERIAL,
intsystem INTEGER NOT NULL REFERENCES yuksystems(id) CONSTRAINT
int_cannot_equal_ext
CHECK (intsystem != extsystem),
extsystem INTEGER NOT NULL REFERENCES yuksystems(id) CONSTRAINT
ext_cannot_equal_int
CHECK (extsystem != intsystem),
PRIMARY KEY (intsystem, extsystem)
);

the intsystem and extsystem fields both have a check constraint on them
which preventing any one record from having values in which they are
equal. There is also a primary key. Is this redundant? Do only one of
them really need this constraint? Or does it not really matter. I'm
concerned about using constraints like this and have redundant checks
built in slowing down my db.

Ferindo