β 1 , β i , and β n are auxiliary trees that all adjoin at the address g in the elementary tree τ. derivations specify the order in which adjunction takes place (e.g., β 2 adjoins to β 1 and the result to α).
if β 2 adjoins to β 1 , there is only one possible derived tree-namely, a tree where β 2 appears above β 1 .