let p, q be ExtReal; :: thesis: for s being Real st p <= q holds
].-infty,q.[ \ [.p,s.[ = ].-infty,p.[ \/ [.s,q.[
let s be Real; :: thesis: ( p <= q implies ].-infty,q.[ \ [.p,s.[ = ].-infty,p.[ \/ [.s,q.[ )
s in REAL by XREAL_0:def 1;
hence ( p <= q implies ].-infty,q.[ \ [.p,s.[ = ].-infty,p.[ \/ [.s,q.[ ) by Th301, XXREAL_0:12; :: thesis: verum