matita/matita/contribs/lambda/paths/standard_precedence.ma

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  14
  15 include "paths/path.ma".
  16
  17 (* STANDARD PRECEDENCE ******************************************************)
  18
  19 (* Note: standard precedence relation on paths: p ≺ q
  20          to serve as base for the order relations: p < q and p ≤ q *)
  21 inductive sprec: relation path ≝
  22 | sprec_nil : ∀o,q.   sprec (◊) (o::q)
  23 | sprec_rc  : ∀p,q.   sprec (dx::p) (rc::q)
  24 | sprec_sn  : ∀p,q.   sprec (rc::p) (sn::q)
  25 | sprec_comp: ∀o,p,q. sprec p q → sprec (o::p) (o::q)
  26 | sprec_skip:         sprec (dx::◊) ◊
  27 .
  28
  29 interpretation "standard 'precedes' on paths"
  30    'prec p q = (sprec p q).
  31
  32 lemma sprec_inv_sn: ∀p,q. p ≺ q → ∀p0. sn::p0 = p →
  33                     ∃∃q0. p0 ≺ q0 & sn::q0 = q.
  34 #p #q * -p -q
  35 [ #o #q #p0 #H destruct
  36 | #p #q #p0 #H destruct
  37 | #p #q #p0 #H destruct
  38 | #o #p #q #Hpq #p0 #H destruct /2 width=3/
  39 | #p0 #H destruct
  40 ]
  41 qed-.
  42
  43 lemma sprec_fwd_in_whd: ∀p,q. p ≺ q → in_whd q → in_whd p.
  44 #p #q #H elim H -p -q // /2 width=1/
  45 [ #p #q * #H destruct
  46 | #p #q * #H destruct
  47 | #o #p #q #_ #IHpq * #H destruct /3 width=1/
  48 ]
  49 qed-.