Certainty Effect
If you prefer A to B, then .5U($50) > .7U($30)
Dividing both sides by .7 gives .7143U($50) > U($30)

But if you prefer D to C, then .8U($50) < U($30)

Prferring E to F is in line with Von Neumann and Morgenstern,
but simulataneously preferring A to B AND D to C is not.

The line after the statement of alternatives E and F shoud say
"According to EU EV, people should be indifferent between E and F, becaose they both have the same  EU EV"

The statement "Prospect theory assumes that losses have greater weight than gains, which explains why people tend to be risk seeking for losses but not for gains" is a non sequitur.
The point is that increasing gains have decreasing marginal utility, increasing losses have decreasing marginal disutility.
In money terms, prospect theory focuses on cash flow while Von Neumann and Morgenstern focus on wealth.
According to prospect theory, doubling a cash flow has less than twice the effect the original cash flow would have; gaining $2 is less than twice as pleasurable as gaining $1, losing $2 is less than twice as painful as losing $1.