CAS command question

[DrD]

CAS commands left() and right() are described to return the left or right side of an expression.
(With assurance I can say that these two CAS commands are bug free).

Going confidently forward :

Here is a list of string object expressions in L9, such that a polynomial is always on the left side, and a constant is always on the right side. For each of the expressions, using the CAS left() command results in list L8, the left side of each expression. Since the CAS left() and right() commands operate correctly, the program result, L8, assuredly, contains the polynomials that are on the left, right?
(using the CAS right() works equally well.)

Snippet: L9:={"x+y=4", "x+y>4","x+y>=4","x+y<4","x+y<=4"};
Left side of L9 expressions (and don't bet your life on it ...): L8 ==> {x+y,x+y,x+y,4,4}

Discussion is welcome.

Code:


EXPORT lefty()
BEGIN
  L8:={};L9:={"x+y=4", "x+y>4","x+y>=4","x+y<4","x+y<=4"};
  //  Make a list of ->left side<- ONLY for expressions in L9
  FOR I FROM 1 TO SIZE(L9) DO
    L8(I):=CAS("left(CAS(L9(I)))");  
  END;   
END;

-Dale-