Erythrogenic acid, C₁₈H₂₆O₂, is an acetylenic fatty acid that turns a vivid red on exposure to light. On catalytic hydrogenation over a palladium catalyst, 5 equivalents of H₂ is absorbed, and stearic acid, CH₃ (CH₂) ₁₆CO₂H, is produced. Ozonolysis of Erythrogenic acid gives four products: formaldehyde, CH₂O; oxalic acid, HO₂CCO₂H; azelaic acid, HO₂C (CH₂) ₇CO₂H; and the aldehyde acid OHC (CH₂) ₄CO₂H. Draw two possible structures for Erythrogenic acid, and suggest a way to tell them apart by carrying out some simple reactions.