Help with PLPGSQL syntax please

Could someone please tell me the correct syntax for the following problem in
plpgsql:

The following expression code sample works but now (for example) I'd like to
subsitute
the variables $1 and $2 for the numbers 0 and 2 in the following
expression:

INSERT INTO rtest(xz,yz,xy) VALUES ( \'(0,2), (1,3)\',
\'(1,2),
(2,3)\',
\'(0,1),
(1,2)\');

What's the correct way of represinting the strings?

A complete code example is below. It's to do with the usage of R-tree
indexing.

Eddy
edward(dot)grabczewski(at)btinternet(dot)com
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DROP TABLE rtest;
DROP INDEX rtest_xz_index;
DROP INDEX rtest_yz_index;
DROP INDEX rtest_xy_index;

CREATE TABLE rtest (
xz BOX,
yz BOX,
xy BOX);

CREATE INDEX rtest_xz_index ON rtest USING RTREE (xz bigbox_ops);
CREATE INDEX rtest_yz_index ON rtest USING RTREE (yz bigbox_ops);
CREATE INDEX rtest_xy_index ON rtest USING RTREE (xy bigbox_ops);

DROP FUNCTION threedpoint (float,float,float, float,float,float);
CREATE FUNCTION threedpoint (float,float,float,float,float,float)
RETURNS text
AS 'DECLARE
x1 ALIAS FOR $1;
y1 ALIAS FOR $2;
z1 ALIAS FOR $3;
x2 ALIAS FOR $4;
y2 ALIAS FOR $5;
z2 ALIAS FOR $6;
BEGIN
INSERT INTO rtest(xz,yz,xy)
VALUES ( \'(0,2), (1,3)\',
\'(1,2), (2,3)\',
\'(0,1), (1,2)\');
RETURN null;
END;'
LANGUAGE 'plpgsql';

SELECT threedpoint(100,200,300,400,500,600);

SELECT * FROM rtest
ORDER BY xz USING <<;

SELECT xz, yz, xy FROM rtest
WHERE xz @ '(1.0,3.0),(0.0,2.0)'::box
AND yz @ '(2.0,3.0),(1.0,2.0)'::box
AND xy @ '(1.0,2.0),(0.0,1.0)'::box
ORDER BY xz USING <<;

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