How to show $L = \{a^n b^m c^p: n\neq m\} \cup \{a^n b^m c^p: m\neq p\}$ is ambiguous?

Question

I'm recently familiar with this site and prefer to ask a very hard problem :)

How can we prove that the following language is inherently ambiguous?

$$L = \{a^n b^m c^p: n\neq m\} \cup \{a^n b^m c^p: m\neq p\}$$

this is an example in my note without a proof.