let t be ExtReal; :: thesis: for s being Real holds ].-infty,t.[ \ ].-infty,s.] = ].s,t.[
let s be Real; :: thesis: ].-infty,t.[ \ ].-infty,s.] = ].s,t.[
s in REAL by XREAL_0:def 1;
hence ].-infty,t.[ \ ].-infty,s.] = ].s,t.[ by Th187, XXREAL_0:12; :: thesis: verum