A surfer with a large white surfboard and tether line is standing on the beach on an overcast day .
It is certain that a surfer with a large purple surfboard and tether line is standing on the beach on an sunny day .
It is impossible that a surfer with a large purple surfboard and tether line is standing on the beach on an sunny day .
It is certain that a surfer with a large purple surfboard and tether line is standing on the beach on an sunny day .
A surfer with a large purple surfboard and tether line is standing on the beach on an sunny day .