プログラム学習・有機化学 Organic chemistry Programmed Study

Decalin C₁₀H₁₈ which is equivalent to the hydride of naphthalene has the structure that two cyclohexane rings are condensed with each other at one side. How many geometrical isomers exist for decalin, supposing that the two cyclohexane rings in decal in keep the chair form?