ACL2-PC_colon__colon_CONTRAPOSE.html -- ACL2 Version 6.3

### ACL2-PC::CONTRAPOSE

(primitive) `` switch a hypothesis with the conclusion, negating both

    Major Section:  PROOF-CHECKER-COMMANDS

    Example:
    (contrapose 3)

    General Form:
    (contrapose &optional n)

The (optional) argument `n` should be a positive integer that does not exceed the number of hypotheses. Negate the current conclusion and make it the `n`th hypothesis, while negating the current `n`th hypothesis and making it the current conclusion. If no argument is supplied then the effect is the same as for `(contrapose 1)`.

Remark: By ``negate'' we mean an operation that replaces `nil` by `t`, `x` by `nil` for any other explicit value `x`, `(not x)` by `x`, and any other `x` by `(not x)`.