Value( f, w )
Let f be a Laurent polynomial (..., f_{-1}, f_0, f_1, ...). Then
Value returns the finite sum ... + f_{-1} <w>^{-1} + f_0 <w>^0 + f_1
<w> + ....
Note that x need not be contained in the base ring of f.
gap> x := Indeterminate(Integers);; x.name := "x";;
gap> k := -x + 1;
-x + 1
gap> Value( k, 2 );
-1
gap> Value( k, [[1,1],[0,1]] );
[ [ 0, -1 ], [ 0, 0 ] ]
GAP 3.4.4