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Subst

substitute values for indeterminates
Syntax 

Subst(E:OBJECT, X, F):OBJECT
Subst(E:OBJECT,[[X_1, F_1],...,[X_r, F_r]]):OBJECT

where each X or X_i is an indeterminate and each F or F_i is a number,
polynomial, or rational function.

Description
The first form of this function substitutes F_i for X_i in the expression E. The second form is a shorthand for the first in the case of a single indeterminate. When substituting for the indeterminates in order, it is easier to use Eval .

Example 
  Use R ::= QQ[x,y,z,t];
  F := x+y+z+t^2;
  Subst(F,x,-2);
t^2 + y + z - 2
-------------------------------
  Subst(F,x,z/y);
(yt^2 + y^2 + yz + z)/y
-------------------------------
  Subst(F,[[x,x^2],[y,y^3],[z,t^5]]);
t^5 + y^3 + x^2 + t^2
-------------------------------
  Eval(F,[x^2,y^3,t^5]); -- the same thing as above
t^5 + y^3 + x^2 + t^2
-------------------------------
  MySubst := [[y,1],[t,3z-x]];
  Subst(xyzt, MySubst);  -- substitute into the function xyzt
-x^2z + 3xz^2
-------------------------------


See Also