 The definition of \(\mathbf{GR}\) is also of historical importance because it was the first among several equivalent (and nearly contemporaneous) definitions of what were originally called the recursive functions but are now often referred to as the computable functions (see  Section 2.2).  These developments also contributed to one of the two final chapters in the study of recursive definability prior to the initiation of computability theory as an independent subject—i.e., the isolation and eventual adoption of what is now known as Church’s Thesis.