1.
Let ⋄∈{∧,∨,⇒,⇔}\diamond \in \{\wedge, \vee, \Rightarrow, \Leftrightarrow\} be such that (p⋄q)⇔((p∨q)⋄q)(p \diamond q) \Leftrightarrow ((p \vee q) \diamond q) is a tautology. Then ⋄\diamond is equal to: