let L be Lattice; :: thesis: for p being Element of L holds FinJoin {.p.} = p
let p be Element of L; :: thesis: FinJoin {.p.} = p
thus FinJoin {.p.} = the L_join of L $$ ({.p.},(id L)) by LATTICE2:def 3
.= (id L) . p by SETWISEO:17
.= p by FUNCT_1:18 ; :: thesis: verum