The question in full is to give the answer for X_i when i = 0 for...

X_i = { x 'element_of' N | x is divisible by i }

where i is a natural number.

...maybe he is arguing 'divides' means something different to 'is divisible by'.

He is claiming the answer is the empty set but I reckon it should be {0}.

Whadayathink?