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LIST_INDUCT_TAC                                              (listLib)
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LIST_INDUCT_TAC : tactic

SYNOPSIS
Performs tactical proof by structural induction on lists.

KEYWORDS
tactic, list, induction.

DESCRIBE
{LIST_INDUCT_TAC} reduces a goal {!l.P[l]}, where {l} ranges over lists, to two
subgoals corresponding to the base and step cases in a proof by structural
induction on {l}. The induction hypothesis appears among the assumptions of the
subgoal for the step case.  The specification of {LIST_INDUCT_TAC} is:

                     A ?- !l. P
   =====================================================  LIST_INDUCT_TAC
    A |- P[NIL/l]   A u {{P[l'/l]}} ?- !h. P[CONS h l'/l]

where {l'} is a primed variant of {l} that does not appear free in
the assumptions {A} (usually, {l'} is just {l}). When {LIST_INDUCT_TAC} is
applied to a goal of the form {!l.P}, where {l} does not appear free in {P},
the subgoals are just {A ?- P} and {A u {{P}} ?- !h.P}.

FAILURE
{LIST_INDUCT_TAC g} fails unless the conclusion of the goal {g} has the form
{!l.t}, where the variable {l} has type {(ty)list} for some type {ty}.

SEEALSO
listLib.EQ_LENGTH_INDUCT_TAC, listLib.EQ_LENGTH_SNOC_INDUCT_TAC,
listLib.SNOC_INDUCT_TAC.

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