question: What , if it formed the `` essential basis '' of a state 's consent to a treaty , may invalidate that consent ?
answer: an erroneous understanding of a fact or situation
turker_answer: If it formed the `` essential basis '' of a state 's consent to a treaty , an erroneous understanding of a fact or situation may invalidate that consent .
rule-based: An erroneous understanding of a fact or situation formed the `` essential basis '' of a state 's consent to a treaty , may invalidate that consent .