%SEQUENCE
attr x
meth init x:=nil end
meth isEmpty($) @x==nil end
meth first($) @x.1 end
meth last($) {Nth @x {Length @x}} end
meth insertFirst(X) x:= X|@x end
meth insertLast(X) x:={Append @x X|nil} end
meth removeFirst x:=@x.2 end
meth removeLast
    local L in
        L=@x
        x:=nil
        for I in {Length L}-1..1;~1 do
            x:= {Nth L I}|@x
        end
    end
end

%PALINDROME
S={New Sequence init}
    fun{Check}
        if {S isEmpty($)} then true
        else
            if {S first($)}=={S last($)} then
            {S removeFirst}
            {S removeLast}
            {Check}
            else false end
        end
    end
in
for I in Xs do
      {S insertFirst(I)}
   end
{Check}