 The definition of \(-A\) in terms of \(A \rightarrow \mathbf{0}\) throws up an asymmetry between positive and negative information. In an information model \(-A\) holds at \(x \in \mathbf{F}\) iff \(A\) does not hold at any \(y \in \mathbf{F}\) such that \(x \sqsubseteq y\). Whilst the verification of \(A\) at \(x \in \mathbf{F}\) only involves checking \(x\), verifying \(-A\) at \(x \in \mathbf{F}\) involves checking all \(y \in \mathbf{F}\) such that \(x \sqsubseteq y\). According to Gurevich (1977) and Wansing (1993), this asymmetry means that intuitionistic logic does not provide an adequate treatment of negative information, since, unlike the verification of \(A\), there is no way of verifying \(-A\) “on the spot” so to speak. Gurevich and Wansing’s objection to this asymmetry is a critical response to Grzegorczyk (1964). For arguments in support of Grzegorczyk’s asymmetry between positive and negative information, see Sequoiah-Grayson (2009). A fully constructive negation that allows for falsification “on the spot” is known also as Nelson Negation on account of it being embedded within Nelson’s constructive systems (Nelson 1949, 1959). For a contemporary development of these constructive systems, see section 2.4.1 of Wansing (1993). 