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*Definition:* a *proof rule* reduces a proof situation to one or
more other situations.

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K_{0}G_{0}

K_{1}G_{1}

"In order to prove `G`_{0} with knowledge `K`_{0} it suffices to
prove `G`_{1} with knowledge `K`_{1}".

*Definition:* a *proof*
is the reduction of the start situation to other situations that are again
reduced to other situations until we have only situations in which nothing is
left to be proved.

Author: Wolfgang Schreiner

Last Modification: November 30, 1999