SET-BACKCHAIN-LIMIT.html -- ACL2 Version 6.3

## SET-BACKCHAIN-LIMIT

sets the backchain-limit used by the type-set and rewriting mechanisms

    Major Section:  SWITCHES-PARAMETERS-AND-MODES

Note: This is an event! It does not print the usual event summary but nevertheless changes the ACL2 logical world and is so recorded. Moreover, its effect is to set the `acl2-defaults-table`, and hence its effect is `local` to the book or `encapsulate` form containing it; see acl2-defaults-table.

This event sets the global `backchain-limit` used by the ACL2 type-set and rewriting mechanisms. Its value may be a cons whose car and cdr are each either `nil` or a non-negative integer. Its value `x` may also be `nil` or a non-negative integer, which is treated as a cons whose car and cdr are both `x`.

The car is used to limit backchaining used by the ACL2 type-set mechanism, while the cdr is used to limit backchaining used by the rewriting mechanism. See backchain-limit for details about how backchain-limits are used. Rewrite backchain limits may also be installed at the level of hints; see hints for a discussion of `:backchain-limit-rw`.

    :set-backchain-limit nil  ; do not impose any additional limits
    :set-backchain-limit 0    ; allow only type-set reasoning for rewriting
                              ; hypotheses
    :set-backchain-limit 500  ; allow backchaining to a depth of no more
                              ; than 500 for rewriting hypotheses
    (set-backchain-limit 500) ; same as above
    :set-backchain-limit (500 500)
                              ; same as above
    (set-backchain-limit '(500 500))
                              ; same as above
    (set-backchain-limit '(3 500))
                              ; allow type-set backchaining to a depth of no more
                              ; than 3 and rewriter backchaining to a depth of no
                              ; more than 500

The default limit is `(nil nil)`.