Using this as an opportunity to grind an axe (not your fault, cactusfrog!): I find it clearer when people write "not every X is a Y" than "every X is not a Y", which could be (and would be, literally) interpreted to mean the same thing as "no X is a Y".
Using this as an opportunity to grind an axe (not your fault, cactusfrog!): I find it clearer when people write "not every X is a Y" than "every X is not a Y", which could be (and would be, literally) interpreted to mean the same thing as "no X is a Y".