Trinisphere v.s. Buyback

[+t]

My question is if trinisphere affects a buybacked shattering pulse.  I am 99% sure that it would cost 5R (the cmc would be raised by 1), while my friend swears that it would cost 4R to cast.

Who is right here?

[DEA]

you are 99% wrong here
trinisphere doesn't care what the cmc is
it just looks at what you pay and if it's more than 3, trinisphere just does nothing
as buyback on pulse is 4R, trinisphere does nothing to it