@article(buchi1960weak,
 author       = {J Richard B{\"u}chi},
 year         = {1960},
 title        = {Weak Second-Order Arithmetic and Finite Automata},
 journal      = {Mathematical Logic Quarterly},
 volume       = {6},
 number       = {1-6},
 pages        = {66--92},
 doi          = {10.1002/malq.19600060105},
)
@article(buchi1960decision,
 author       = {B\IeC{\"u}chi, J. Richard},
 year         = {1960},
 title        = {On a Decision Method in Restricted Second Order Arithmetic},
 pages        = {425--435},
 doi          = {10.1007/978-1-4613-8928-6_23},
)