[請益] 又是命題邏輯

[william0612 (Will)]

想請教高手

1.) Prove A v A v A |- B -> A

下面應該是屬於論述邏輯? (Predicate Logic)

2.) |- (for all x)(A -> B -> C) -> (for all x)(A -> B) -> (for all x)(A -> C)

3.) Prove by induction on terms, that for any terms t and s,
    if s is a prefix of t, then the strings t and s must be identical.


我承認是問功課....

但我真的想不出來要怎麼證明?..... 第一題只有一邊有B 是要怎麼搞 Orz.....

題外話 學期快結束了 我還真好奇我怎麼存活到現在 囧..

感謝各位的幫忙 T_T

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gon hit as hard as life. But it ain't about how hard u hit. It's about how hard
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then go out n get what u'r worth. But u gotta be willing to take the hit, n not
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◆ From: 76.66.133.182
→ william0612:第一題,我在想是不是用soundness?
推 somedoubt:A→(B→A)
→ somedoubt:(AvA)→(B→A)
→ somedoubt:(Av(AvA))→(B→A)
推 wilo:第一題不能用PC規則啦 :P  那是後設的東西
→ wilo:不過你這邊證明的括號很不嚴謹 :Q
→ wilo:我是說題目 ^^;