14 lines
711 B
Text
14 lines
711 B
Text
inductive term : Type
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| var : nat → term
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| app : string → list term → term
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/- In the current system, it will be hard to work with mutually inductive predicates.
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Reason: we cannot use well-founded recursion, and the induction principle for it
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is too weak. -/
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mutual inductive var_occ, var_occ_list
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with var_occ : nat → term → Prop
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| leaf (n : nat) : var_occ n (term.var n)
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| app (n : nat) (s : string) (ts : list term) : var_occ_list n ts → var_occ n (term.app s ts)
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with var_occ_list : nat → list term → Prop
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| head (n : nat) (t : term) (ts : list term) : var_occ n t → var_occ_list n (t::ts)
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| tail (n : nat) (t : term) (ts : list term) : var_occ_list n ts → var_occ_list n (t::ts)
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