Hello,

the task is to show that the following set of connectives isn't (functionally) complete: $\displaystyle \{ \vee, \wedge, \rightarrow, \leftrightarrow, \top \}$

I know that the negation connective can't be expressed with those, but the problem is how to prove that. I tried to roll some truth tables, but that didn't help. I think some kind of inductive proof is needed.

Any help is appreciated, thank you very much!