let a, b be Element of ExWALattice; :: thesis: ( a = 1 & b = 2 implies a "\/" b = 2 )
reconsider aa = a, bb = b as Element of {0,1,2,3,4} ;
assume A1: ( a = 1 & b = 2 ) ; :: thesis: a "\/" b = 2
a "\/" b = aa ex1234"\/" bb by EXUDef
.= max (aa,bb) by A1, UPDef ;
hence a "\/" b = 2 by A1, XXREAL_0:def 10; :: thesis: verum