* Alonzo Church, "An unsolvable problem of elementary number theory", American Journal of Mathematics, 58 (1936), pp 345–363* Alonzo Church, "A note on the Entscheidungsproblem", Journal of Symbolic Logic, 1 (1936), pp 40–41.
* Alonzo Church, «An unsolvable problem of elementary number theory», American Journal of Mathematics, 58 (1936), pp 345—363* Alonzo Church, «A note on the Entscheidungsproblem», Journal of Symbolic Logic, 1 (1936), pp 40-41.