First test and initial setup
Added test where two numbers exist in the phone book and one is a subset of the other
Refactoring - function extraction - subset comparison
Refactoring - function extration  for subset matching indication search
Refactoring - removed an else branch by setting Z to consistent by default
Refactoring - removed yet another else branch by setting Z to consistent,
further up the flow
Renaming a function to make it more literate
Refactoring - put the boolean expression in a method for literacy
More refactoring - removal of temporary variable.
Changed name of one function slightly so as to fit better in a sentence
Added third test - with three numbers in the phone book and they are consistent