Let HA and PA denote Heyting and Peano arithmetic, respectively, let N be the standard natural numbers, and let PL(T,U) and PLΣ1(T,U) denote the provability logics of U with respect to T, using arbitrary and Σ1 substitutions, respectively. Write iH for the intuitionistic provability logic of HA, iH∗ for the logic defined in the cited work, iHP for iH extended by P, and iHSP for iH extended by S and P. The notations iHσ, iHσP, iHσSP, and iHσ∗∗ are the corresponding Σ1-substitution logics.
Characterizations and reductions conjecture. The following characterizations and reductions hold:
iH=PL(HA,HA)≤PLΣ1(HA,HA)=iHσ.
iH=PL(HA,HA)≤PL(HA,N)=iHSP.
iHP=PL(HA,PA)≤PLΣ1(HA,PA)=iHσP.
iHSP=PL(HA,N)≤PLΣ1(HA,N)=iHσSP.
iH∗=PL(HA∗,HA∗)≤PLΣ1(HA∗,HA∗)=iHσ∗∗.
Moreover, all these reductions are computable, and consequently all the provability logics are decidable.