Estoppel
117.  When one person has by his declaration, act or omission intentionally caused or permitted another person to believe a thing to be true and to act upon such belief, otherwise than but for that belief he would have acted, neither he nor his representative in interest shall be allowed in any suit or proceeding between himself and such person or his representative in interest to deny the truth of that thing.
Illustration
     A intentionally and falsely leads B to believe that certain land belongs to A and thereby induces B to buy and pay for it.
     The land afterwards becomes the property of A and A seeks to set aside the sale on the ground that at the time of the sale he had no title.
     He must not be allowed to prove his want of title.