Proof: Parallel Lines are Symmetric

Let's prove the following theorem:

if AB || CD, then DC || BA

A B C D

Proof:

View as a tree | View dependent proofs | Try proving it

Given
1 AB || CD
Proof Table
# Claim Reason
1 CD || AB if AB || CD, then CD || AB
2 DC || BA if CD || AB, then DC || BA

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