 The objects in CL are called terms.[9] Terms may be thought to be interpreted as functions (as further explained in section 4.1). Primitive terms comprise variables and constants, whereas compound terms are formed by combining terms. Usually, a denumerable set (i.e., a set with cardinality \(\aleph_0\)) of variables is included, and the constants include some (undefined) combinators. (We use \(x,y,z,v,w,u,x_0,\ldots\) as variables in the object language, and \(M,N,P,Q,\ldots\)  as metavariables that range over terms.)