I am reading Part II of Chin and Tarski's "Distributive and Modular Laws in the Arithmetic of Relation Algebras". In the beginning of section 4, the authors say "In general, if $\odot$ is a binary operation which is commutative, associative, and tautological, then both the left and right distributive laws for $\odot$ under $\odot$ are identically satisfied". My question is: what does "tautological" mean in this context?
We are working within a fixed Boolean algebra $B$. $\odot$ is some binary operation on the universe of $B$. He is saying that if $\odot$ is commutative, associative, and "tautological", then $\odot$ is left and right distributive over $\odot$, i.e., for all $x$, $y$, and $z$ in the universe of $B$, $x\odot (y\odot z)=(x\odot y)\odot (x\odot z)$ and $(y\odot z)\odot x=(y\odot x)\odot (z\odot x)$. I can't find the word "tautological" (in reference to a binary relation) used anywhere else.