Zevachim 50 - Chains of Rules of Torah Learning?
Of the thirteen rules of learning the Torah , we want to take four, and find out whether they can be combined. The rules are "same aspect," "same word," a fortiori logic, and a general rule. There are thus 4 rules and 16 possible combinations of them, and the Talmud considers all 16 to see if they can combine.
Let's look at the "same aspect" rule. If the Torah compared two situations and said, "just as...so is" - then this is the "same aspect" rule, and we can learn the laws of one from the other. However, the "same aspect" derivations cannot be chained. If something is learned by comparison of its aspect to another, it cannot turn around and teach us other laws. Why not? We see this from the following situation: the Torah compared sin offering to burnt offering; it also compared a guilt offering to a sin offering. One would expect that we can make this chain deduction: sin offering is similar to burnt offering, guilt offering is similar to a sin offering, therefore guilt offering is similar to burnt offering. However, Torah explicitly taught the comparison of guilt offering to burnt offering, to teach us that the "same aspect" rules are not transitive.
Art; Pieter the Elder Bruegel - Two Chained Monkeys