The antecedent (``if part'') of a rule is usually a conjunction of conditions, using the EMYCIN $AND function:

($AND (SAME CNTXT GRAM GRAMNEG) 
      (SAME CNTXT MORPH COCCUS))

$AND operates as follows:

1. If any clause is false ( nil) or has CF .2 , $AND returns false ( nil). Thus, .2 is used as a cutoff threshold. Any data believed less strongly than .2 is considered to be false.
2. If every clause has CF > .2, $AND returns the minimum of the clause CF values.

There is also a function $OR that returns the maximum of its argument CF values.

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