In reply to @darrenjw
@darrenjw interestingly, this (ftp.cs.wisc.edu/Approx/empty.p…) claims Bourbaki only defined a single 'empty matrix'. I can see people fudging the distinction pre-computers
In reply to @christianp
@darrenjw I can make a devil's advocate case for them all being the same thing if you only look at multiplication: the product of any matrix with the empty matrix is the empty matrix