Modify iset.mm pm2.85 and orimdi for decidability.
Modify iset.mm pm2.85 and orimdi for decidability.

- Replace pm2.85 with pm2.85dc and orimdi with orimdidc. In both
  cases the difference is a decidability requirement, and the proofs
  are modified accordingly.

metamath/set.mm,metamath/set.mm,metamath/set.mm