take [ the set , the set , the set ] ; :: thesis: [ the set , the set , the set ] is triple
take the set ; :: according to XTUPLE_0:def 5 :: thesis: ex x2, x3 being object st [ the set , the set , the set ] = [ the set ,x2,x3]
take the set ; :: thesis: ex x3 being object st [ the set , the set , the set ] = [ the set , the set ,x3]
take the set ; :: thesis: [ the set , the set , the set ] = [ the set , the set , the set ]
thus [ the set , the set , the set ] = [ the set , the set , the set ] ; :: thesis: verum