b ∧ (b ∨ c ∨ d ) ∧ d ∧ ( a ∨ b ∨ d ) ∧ ( a ∨ b ∨ c ∨ d )=(b ∧ (b ∨ (c ∨ d ))) ∧ d ∧( ( a ∨ b ∨ d ) ∧ (( a ∨ b ∨ d) ∨ d) )=b ∧ d ∧( a ∨ b ∨ d)=b ∧ (d ∧( d ∨( b ∨ a)))= b ...