# De Morgan's Law

Sometimes it can be confusing to think about boolean expressions with
not's and or's.
For example

If the value is not 2 or not 3 then ...

if translated literally from English, becomes :
if ((v != 2) || (v != 3)) ...

which is **ALWAYS TRUE**
what we really want is:

if ((v != 2) && (v != 3)) ...

You can always use some tautologies to simplify things.

#### De Morgan's law

- not(P and Q) is equivalent to
(not P) or (not Q)
- not(P or Q) is equivalent to
(not P) and (not Q)

#### from the meaning of not