proofManagerLib.backup

STRUCTURE

SYNOPSIS

Restores the proof state, undoing the effects of a previous expansion.

DESCRIPTION

The function backup is part of the subgoal package. It may be abbreviated by the function b. It allows backing up from the last state change (caused by calls to expand, rotate and similar functions). The package maintains a backup list of previous proof states. A call to backup restores the state to the previous state (which was on top of the backup list). The current state and the state on top of the backup list are discarded. The maximum number of proof states saved on the backup list can be set using set_backup. It defaults to 15. Adding new proof states after the maximum is reached causes the earliest proof state on the list to be discarded. The user may backup repeatedly until the list is exhausted. The state restored includes all unproven subgoals or, if a goal had been proved in the previous state, the corresponding theorem. For a description of the subgoal package, see set_goal.

FAILURE

The function backup will fail if the backup list is empty.

EXAMPLE

- g `(HD[1;2;3] = 1) /\ (TL[1;2;3] = [2;3])`;
> val it =
    Proof manager status: 1 proof.
    1. Incomplete:
         Initial goal:
         (HD [1; 2; 3] = 1) /\ (TL [1; 2; 3] = [2; 3])

     : proofs

- e CONJ_TAC;
OK..
2 subgoals:
> val it =
    TL [1; 2; 3] = [2; 3]


    HD [1; 2; 3] = 1

     : proof

- backup();
> val it =
    Initial goal:

    (HD [1; 2; 3] = 1) /\ (TL [1; 2; 3] = [2; 3])

     : proof

- e (REWRITE_TAC[listTheory.HD, listTheory.TL]);
OK..
> val it =
    Initial goal proved.
    |- (HD [1; 2; 3] = 1) /\ (TL [1; 2; 3] = [2; 3]) : proof

USES

Back tracking in a goal-directed proof to undo errors or try different tactics.

SEEALSO

set_goal, restart, backup, restore, save, set_backup, expand, expandf, p, top_thm, top_goal