I was somehow challenged by the idea: do more abstract topics allow proofs without words? I came out with this example. Of course, it is disputable if it is really "without words", since some words of explanation should be given (here they are: vertical segments represent Banach spaces and subspaces; parallel connecting segments between them represent bijective linear maps, segments to the point $0$ represent zero linear maps. Italic letters $a,b,c,d,e$ are dimensions of finite dimensional linear subspaces ).
