This is a prover for KLM ( Kraus, Lehmann and Magidor ) logic P as defined in:

L Gordano, V Gliozzi, N Olivetti, G Pozzato

"Analytic tableaux for KLM Preferential and Cummulative Logic"

Proceedings of LPAR 2005 LNAI 3835:666-681, Springer, 2005.

When you enter a formula A, then "closed" means that A is a

theorem because the tableau for ~ A is closed, and "open" means

that it is not a theorem because the tableau for ~ A is open.