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The truth-deriving procedures Llull suggested were mainly two. One
proceeded in the positive sense: concepts were combined (following the
directing graphs) and, if mutually reinforcing, they proved the
conclusion "by analogy". The negative dual was that at some point
the concepts that were being currently manipulated turned out to be
mutually inconsistent (contradictory); that meant that the initial
postulated truth was automatically disproved, thereby proving the
contrary. This is the first appearance in the literature of something
not unlike Beth's 1955 semantic tableaux (or Popper's 1959
refutational ideas in Science). It is, however, a mere
l3th-century anticipation of present-day developments, which
-unlike all the other insights mentioned- have not been directly
influenced by Llull's ideas or by Leibniz's rendition of them.
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