(p+q)*(p→r)*(q→r) = (p+q)*('p+r)*('q+r)
=(p+q)*('p*'q + 'p*r + 'q*r + r)
=(p+q)*('p*'q + r)
=(p+q)*('(p+q) +r)
=(p+q)*'(p+q) + (p+q)*r
= 0 + (p+q)*r = (p+q)*r
何か変なところある？