What does this Prolog list manipulation program do?

Question

I\'m trying to wrap my head around this:

r([], _, []).
r([a(H,_)|T], a(H,X), [a(H,X)|T]).
r([a(H,V)|T], a(I,L), [a(H,V)|R]) :-
    H \\= I,
    r(T, a(I,L), R