Checking a set of patterns against the database

Just as ALLADD and ALLREMOVE can be given a list of patterns to add or remove, similarly, ALLPRESENT can be given a list of patterns to look for in the database. If it finds items for all of them it returns a list of the found items (and also assigns it to the variable THEM). Otherwise its result is false. E.g. to find a grandson of TOM:

    alladd([
          [dick father harry]
          [tom father jack]
          [bill father tom]
          [jack father dick]]);

    vars x, y;
    if allpresent([[tom father ?x] [?x father ?y]]) then
      y =>
    endif;
    ** dick
    them =>
    ** [[tom father jack] [jack father dick]]

    HELP DATABASE,  HELP ADD,   HELP PRESENT,
    HELP REMOVE,    HELP FLUSH, HELP LOOKUP.
    HELP FOREACH,   HELP FOREVERY