public override int lambda(Stack st)
{
int narg = getNarg(st);
Algebraic x = getAlgebraic(st);
Algebraic index_in = CreateVector.crv(st);
if (index_in.constantq())
{
Matrix mx = new Matrix(( Algebraic )x);
Index idx = Index.createIndex(index_in, mx);
mx = mx.extract(idx);
x = mx.reduce();
}
else
{
MatRef mr = new MatRef(( Algebraic )x);
x = new Polynomial(new FunctionVariable("MR(" + x + ")", index_in, mr));
}
st.Push(x);
return(0);
}