matita/matita/contribs/lambdadelta/delayed_updating/etc/lift/fsubst.etc

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  14
  15 include "delayed_updating/syntax/prototerm.ma".
  16 include "delayed_updating/notation/functions/pitchforkleftarrow_3.ma".
  17
  18 (* FOCALIZED SUBSTITUTION ***************************************************)
  19
  20 definition fsubst (p) (u): prototerm → prototerm ≝
  21            λt,q.
  22            ∨∨ ∃∃r. r ϵ u & p●r = q
  23             | ∧∧ q ϵ t & (∀r. p●r = q → ⊥)
  24 .
  25
  26 interpretation
  27   "focalized substitution (prototerm)"
  28   'PitchforkLeftArrow t p u = (fsubst p u t).