Predicates for handling preferences

• name/1 is used for naming rules.

  This literal must occur as the first body literal, if present.

  Alternatively, one may use [mymostpreferredrule] instead of name(mymostpreferredrule).

• </2 is used for indicating preference among different rules (sets of rules).
• \</2 allows to express negated preference.

  That is, r \< s is equivalent to neg (r < s) .