View content where current user is neither author nor comment author

Hello
I'm trying to create a view of content which would display to a logged-in user all the content of a particular type where:
a) the user has not read the content yet
b) AND the user is not the author of the content
c) OR the user is not the author of the last comment
I have managed to get a) and b) working, but I'm stuck trying to add in c) and would be very grateful for some suggestions