When applied to theorems A1 |- t1, ..., An |- tn and a theorem which is a
chain of implications with the successive antecedents the same as the
conclusions of the theorems in the list (up to alpha-conversion),
A |- t1 ==> ... ==> tn ==> t, the LIST_MP inference rule performs a chain
of MP inferences to deduce A u A1 u ... u An |- t.
A1 |- t1 ... An |- tn A |- t1 ==> ... ==> tn ==> t
--------------------------------------------------------- LIST_MP
A u A1 u ... u An |- t