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Syntax: [or <predication>*]

OR sequentially searches, from the left to the right,
for the solutions of the predications. If OR is
finished, it will return the solutions of all the
predications and an unusable value.
Statements can have the values True, False and
Unknown. The following table shows, how OR functions:

  |  or |  T  |  F  |  U  |
  |  T  |  T  |  T  |  T  |
  |  F  |  T  |  F  |  U  |
  |  U  |  T  |  U  |  U  |

Example: >(ask [or
               [options SIEMENS-NIXDORF _options]
               [options WANG _options]]
               (kb-format "~% ~A" (name-of _options)))

First the interpreter searches for the bindings of
the first predication, then for the links of the
second and then it returns all links which it found.

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