6. If the statement is true, prove it. If the statement is false, disprove it (this may or may not involve giving a counterexample).
In an Integral Domain, every irreducible element is prime. In an Integral Domain, every prime element is irreducible. In the ring Z[i], the ideal I = {a + bi | a,b ∈ 2Z} is prime. If R is a PID, then R[z] is also a PID.