When a geometry is described by a set of axioms, the notion of a line is usually left undefined (a so-called primitive object). The properties of lines are then determined by the axioms which refer to them.
Definition of mull 1: friable forest humus that forms a layer of mixed organic matter and mineral soil and merges gradually into the mineral soil beneath 2: a finely powdered solid especially in a suspension
A: A cull cow is any cow that has left the herd. The term culling is most often associated with the deliberate killing of undesirable cattle, but it also refers to animals that are sold off alive for any reason and those that die naturally while still on the farm.