LIST_CONJ : (thm list -> thm)
A1 |- t1 ... An |- tn ---------------------------------- LIST_CONJ A1 u ... u An |- t1 /\ ... /\ tn
LIST_CONJ does not check for alpha-equivalence of assumptions when forming their union. If a particular assumption is duplicated within one of the input theorems assumption lists, then it may be duplicated in the resulting assumption list.