Hasse diagram

Etymology
Named after Helmut Hasse (1898–1979), though he was not the first to use them.

Noun

 * 1)  A diagram which represents a finite poset, in which nodes are elements of the poset and arrows represent the order relation between elements. Transitivity of the order relation is tacit, in other words, if $$ x \le y$$ and $$y \le z $$ then no arrow is drawn from x to z, but if there is no distinct z between x and y (such that $$ x \le z \le y $$) then an arrow is draw from x to y.