Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**samuel12****Member**- Registered: 2010-07-17
- Posts: 19

I'm having a few troubles with 'validly deduce'

Here is the question:

Q: For any set S of sentences, if T is a tautology, then you can validly deduce T from S.

Can anyone explain to me what it is to 'validly deduce' something, pretty confused here, cheers

Offline

**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

T is a tautology, so it's always true. Therefore, you can always deduce it no matter what facts you start with.

For example, this is a valid deduction:

"If it rains tomorrow, then 3 is less than 7."

Why did the vector cross the road?

It wanted to be normal.

Offline