let a, b be Element of ExWALattice; :: thesis: ( b = 4 implies a "/\" b = a )
reconsider aa = a, bb = b as Element of {0,1,2,3,4} ;
A0: ( aa = 0 or aa = 1 or aa = 2 or aa = 3 or aa = 4 ) by ENUMSET1:def 3;
assume A1: b = 4 ; :: thesis: a "/\" b = a
a "/\" b = aa ex1234"/\" bb by EXNDef
.= min (aa,4) by A1, ExMeetDef
.= aa by A0, XXREAL_0:def 9 ;
hence a "/\" b = a ; :: thesis: verum