移除b元素，重新生成新表达式。
(((a & b) & c) & d) ==> ((a & c) & d)
(((a | b) & c) & d) ==> ((a & c) & d)
(((a & b) | c) & d) ==> ((a | c) & d)
(a & b & c & d) ==> (a & c & d)
(a | b & c & d) ==> (a & c & d)
(a & b | c & d) ==> (a | c & d)
((a & b) & (c & d) & (e & f)) ==> (a & (c & d) & (e & f))
((a | b) & (c & d) & (e & f)) ==> (a & (c & d) & (e & f))
((a & b) | (c & d) & (e & f)) ==> (a | (c & d) & (e & f))
