Increasing Certainty

EMYCIN systems sometimes include rules of the form:
A ∧ B → A

Such a rule is logically redundant, but may serve to increase the CF of the conclusion based on additional evidence.

If: 1) The identity of the snake is 
       rattlesnake, and
    2) It bites someone, and 
    3) He dies
Then: There is strongly suggestive 
       evidence (.8) that the identity of 
       the snake is rattlesnake.