Original sentence: Critics (such as Lawrence Lessig in his book Free Culture), have argued that Disney's protection of this copyright is ironic and hypocritical, since Mickey Mouse was first seen in Steamboat Willie, a film clearly based on Buster Keaton's movie Steamboat Bill, Jr
Edited sentence: What is ironic about this is the fact that, as Lawrence Lessig pointed out in his book Free Culture, Mickey Mouse's first appearance on Steamboat Willie is a clear borrowing from Buster Keaton's movie Steamboat Bill, Jr