|\^/|     Maple 6 (SUN SPARC SOLARIS)
._|\|   |/|_. Copyright (c) 2000 by Waterloo Maple Inc.
 \  MAPLE  /  All rights reserved. Maple is a registered trademark of
 <____ ____>  Waterloo Maple Inc.
      |       Type ? for help.
> f := proc(n) if (n=-1) then 0 elif (n=0) then 1
> else f(n-1)+f(n-2); fi; end:
> 
> f := proc(n) if (n=-1) then 0 elif (n=0) then 1
> else f(n-1)+f(n-2); fi; end;
f := proc(n)
    if n = -1 then 0 elif n = 0 then 1 else f(n - 1) + f(n - 2) end if
end proc

> seq(f(n),n=-1..4);
                               0, 1, 1, 2, 3, 5

> addvert:=t->[op(t),V]:
> addhor:=t->[op(t),L,R]:
> Tilings:=proc(n) options remember;
>     if n=-1 then {}
>     elif n=0 then {[]}
>     else {op(map(addvert,Tilings(n-1))),
>           op(map(addhor,Tilings(n-2)))}
>     fi; end:
> seq(Tilings(n),n=-1..4);
{}, {[]}, {[V]}, {[V, V], [L, R]}, {[V, V, V], [L, R, V], [V, L, R]},

    {[V, V, V, V], [L, R, V, V], [V, L, R, V], [V, V, L, R], [L, R, L, R]}

> evalb([1,2]=[2,1]);
                                     false

> evalb({1,2}={2,1});
                                     true