Referential integrity using constant in foreign key

I need to create referential integrity constraints:

CREATE TABLE classifier (
category CHAR(1),
code CHAR(10),
PRIMARY KEY (category,code)  );

-- code1 references to category 1,
-- code2 references to category 2 from classifier table.
CREATE TABLE info (
code1 CHAR(10),
code2 CHAR(10),
FOREIGN KEY ('1', category1) REFERENCES classifier,
FOREIGN KEY ('2', category2) REFERENCES classifier
);

Unfortunately, second CREATE TABLE causes error

ERROR:  syntax error at or near "'1'" at character 171

Any idea how to implement referential integrity for info table ?
It seems that this is not possible in Postgres.

Andrus.