When determining whether or not a party should be estopped, this court has consistently returned to the rule first set out in Gjerstadengen v. Hartzell, 9 N.D. 268, 83 N.W. 230, 232 (1900):The rule as to the requisites of an estoppel in pais as applied to the title to realty which appeals to us as the most equitable to all parties is that announced by Field, J., in Boggs v. Mining Co., 14 Cal. [2