Emphasis, emphasis and more emphasis
Yesterday I came across this one: 쉽지만은 않은 blah blah blah
What draws my attention is the use of 만. Normally to put emphasis on a negative a 는/를 after 지 would suffice, but here the addition of 만은 seems to double the weight on the whole negative.
I am wondering if there is a scale (gradation) of emphasis that forms the basis for this?
Also would it just be OK to say 쉽지만 않은 ***? Is that 은 redundant? Or it is there to force more emphasis again?