Back to School...

A linguistics professor was lecturing his class.
"In English," he explained, "a double negative forms a positive. In some languages, such as Russian, a double negative is still a negative."
"However," the professor continued, "there is no language wherein a double positive can form a negative."
A voice from the back of the room piped up. "Yeah, right."

*     *     *     *     *

An English professor announced to the class; "There are two words I don't allow in my class. One is gross and the other is cool."
From the back of the room a voice called out, "So, what are the words?"