# I don't understand the logic behind lesson 12/17

I got the 3 of them wrong on my first try, and I can’t seem to grasp why Booleans 1, 2 & 3 are “True”, “False” & “True”. Can somebody help me out please?

Combining Boolean Operators

`AND` will only return `true` when all (in this case, both) operands yield `true`.

`OR` will only return `false` when all the operands yield `false`.

``````(3 < 4 || false)  => true

(false || true)   => true

true && true      => true
``````

When reading an `OR` expression, look for the one operand that stands out as `true` and ignore the others.

``````3 < 4  => true
true   => true
``````

An OR expression is said to short-circuit on true, while an AND expression is said to short-circuit on false. In other words,

``````A || B  needs to be all false to be false

A && B  needs to be all true to be true
``````

Testing this further…

``````!true && (!true || 100 != 5**2)
``````
``````!true && ...
``````

The first operand says it all… false. No point even evaluating any further (the computer doesn’t).

``````true || !(true || false)
``````

Again, the first operand says it all… true. The rest can be ignored.

In order to spot this sort of logic we need to be intimately aware of boolean expressions and their operators so we can tell on sight what is happening. This is meant be all brain mechanics at play.

With that understanding in place we can go back to the example in the lesson,

``````(x && (y || w)) && z
``````

and see in an instant that one of `y` or `w` must be true, along with `x` and `z` or the whole thing is false.

Perfect, thank you so much!

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