00:01
Okay, i want to work out is these two statements.
00:03
The one in black, the one in blue, are equivalent.
00:06
And for that, you use a truth table.
00:09
Well, truth tables with two statements, p and q, always have four lines like this.
00:16
T, t, f, f, f, f, f, f, f, always that order for convenience.
00:22
And what i need first is not q.
00:26
So, let's do that one.
00:29
Q is tf, tf, so not p is f, t, t, t, the reverse of this column.
00:39
Now, next i want to have p implies not q, other words, this item here.
00:48
It implies, what we have is, it's always true unless you see tf.
00:54
So t, t, f is going to be false.
01:02
One is false.
01:05
Here is t, t, that will be true.
01:09
Here is f, f, that will be true.
01:14
And here is f t also.
01:19
So this memorize a fact that would implies this symbol here.
01:24
It's always true unless you see tf.
01:30
Now, then what i do is i work out this one, not q implies p, which means i go from right to left.
01:39
So not q implies p is from there to there.
01:45
So i'm reading right to left.
01:46
That's very important.
01:48
So the first one is f goes to t, and ft is true.
01:54
So this one will be true.
01:57
Let's put it up here, not q implies p.
02:02
And then the next one will be t going to t...