Since this is a definition, it works both ways.
"If it is a very tall building, then it is a skyscraper."
"If it is a skyscraper, then it is a very tall building."
Put them together into a biconditional format.
"It is a skyscraper if and only if it is a very tall building."
Or
"It is a very tall building if and only if it is a skyscraper."
Either one would work.
Hope this helps!
