Contract Relationship issue where relationship can/ can't be swapped

Are the following two relationships considered as duplicates?

OriginalContractId     DestContractId       RelationshipType
A                                B                             C
B                                A                             C

Answer

Yes, they are duplicated. if you add the relationships as described in the question, you will get error:

<ErrorMessage>Duplicate record already exists for the following:ContractRelationship</ErrorMessage>

As it's documented in Developer's Guide and Transaction Reference Guide,
"Duplicate Check 

This validator makes sure that the ContractRelationship that is to be added is not a duplicate of an existing ContractRelationship. A ContractRelationship is considered a duplicate if the OrigContractId, DestContractId, and RelationshipType values are found to be identical."

Additionally, OriginalContractId, DestContractId, and RelationshipType are considered as a set of data, it doesn't matter if it's from or to.

Finally, EndDate is not a consideration for Duplicate Check.