7 Limitations

Figure 7 shows three instances of incorrect proofs
from ProoFVer, which highlight some of the well
known limitations in natural logic (Karttunen,
2015; MacCartney, 2009). In Figure 7.i, the claim
uses two negation words, ‘‘neither’’ and ‘‘nor’’,
both of which appear in different spans and lead
to prediction of two negation NatOps. However,
this NatOp sequence nullifies the effect of the
negation NatOp and predicts SUPPORT instead of
REFUTE. Similarly, in Figure 7.ii the adverb ‘‘mis-
takenly’’ negates semantics of the verb. However,
its effect is not captured in the second mutation
ProoFVer- Natural Logic Theorem Proving for Fact Verification