  Taking a combinatorial point of view on cyclotomic polynomials leads to a
larger class of polynomials we shall call the inclusion-exclusion polynomials.
This gives a more appropriate setting for certain types of questions about the
coefficients of these polynomials. After establishing some basic properties of
inclusion-exclusion polynomials we turn to a detailed study of the structure of
ternary inclusion-exclusion polynomials. The latter subclass is exemplified by
cyclotomic polynomials $\Phi_{pqr}$, where $p<q<r$ are odd primes. Our main
result is that the set of coefficients of $\Phi_{pqr}$ is simply a string of
consecutive integers which depends only on the residue class of $r$ modulo
$pq$.
