- 641 名前：１３２人目の素数さん mailto:sage [2012/04/04(水) 19:25:49.97 ]
- >>631
ちょっと表現を変えると
( x＜min(a, max(b, c))＜y ) ＝ ( x＜a ∧ x＜max(b, c) ) ∧ ( a＜y ∨ max(b, c)＜y )
＝ ( x＜a ∧ ( x＜b ∨ x＜c ) ) ∧ ( a＜y ∨ ( b＜y ∧ c＜y ) )
＝ ( ( x＜a ∧ x＜b ) ∨ ( x＜a ∧ x＜c ) ) ∧ ( ( a＜y ∨ b＜y ) ∧ ( a＜y ∨ c＜y ) )
＝ ( x＜min(a, b) ∨ x＜min(a, c ) ) ∧ ( min(a, b)＜y ∧ min(a, c)＜y )
＝ ( x＜max(min(a, b), min(a, c ))＜y )
∴ min(a, max(b, c))＝max(min(a, b), min(a, c ))
