# Exercise 3.29

We use the fact that `(or <e1> <e2>)`

is true if and only if `(not (and (not <e1>) (not <e2>)))`

is true.

In simple english this means that at least one of two predicates is true if and only if these predicates are not both false.

We use the fact that `(or <e1> <e2>)`

is true if and only if `(not (and (not <e1>) (not <e2>)))`

is true.

In simple english this means that at least one of two predicates is true if and only if these predicates are not both false.