gapt.proofs.lk.rules.macros.ExchangeLeftMacroRule.scala Maven / Gradle / Ivy

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General Architecture for Proof Theory

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package gapt.proofs.lk.rules.macros

import gapt.proofs.Ant
import gapt.proofs.SequentIndex
import gapt.proofs.lk.LKProof
import gapt.proofs.lk.rules.ContractionLeftRule
import gapt.proofs.lk.rules.WeakeningLeftRule

/**
 * Move a formula to the beginning of the antecedent, where the main formula is customarily placed.
 *  *          (π)
 *     Γ, A, Γ' :- Δ
 *    --------------
 *     A, Γ, Γ' :- Δ
 * 
 */
object ExchangeLeftMacroRule {
  def apply(subProof: LKProof, aux: SequentIndex): ContractionLeftRule = {
    require(aux isAnt)
    require(subProof.endSequent isDefinedAt aux)
    ContractionLeftRule(WeakeningLeftRule(subProof, subProof.endSequent(aux)), Ant(0), aux + 1)
  }
}