Fix extraction function (fconstr -> FO term):   - Variables are first order only if unapplied   - Unapplied atoms has an empty pure stack (not singleton [empty Zlapp])
Fix extraction function (fconstr -> FO term):
  - Variables are first order only if unapplied
  - Unapplied atoms has an empty pure stack (not singleton [empty Zlapp])

strub/coqmt,strub/coqmt,strub/coqmt