I happened upon the following sentence in a textbook:
'An increase in the number and size of islets is characteristic of infants born to diabetic mothers.
I get that, as the sentence is presented, the singular noun 'increase' is governing the singular verb 'is', but aren't two different 'increases' being described, one in size and one in number?
On another note, I would probably see nothing wrong with 'The love of money and power was his undoing'. I'd imagine a single 'love' that embraces both 'money' and 'power'.
So, what's the rule in matters like this?