let p be ExtReal; :: thesis: for q being Real st p <= q holds
].-infty,q.] \ [.p,q.[ = ].-infty,p.[ \/ {q}
let q be Real; :: thesis: ( p <= q implies ].-infty,q.] \ [.p,q.[ = ].-infty,p.[ \/ {q} )
q in REAL by XREAL_0:def 1;
hence ( p <= q implies ].-infty,q.] \ [.p,q.[ = ].-infty,p.[ \/ {q} ) by Th319, XXREAL_0:12; :: thesis: verum