let S be Subset of (TOP-REAL 2); :: thesis: for C1, C2 being non empty compact Subset of (TOP-REAL 2) st S = C1 \/ C2 holds
S-bound S = min ((S-bound C1),(S-bound C2))
let C1, C2 be non empty compact Subset of (TOP-REAL 2); :: thesis: ( S = C1 \/ C2 implies S-bound S = min ((S-bound C1),(S-bound C2)) )
assume A1: S = C1 \/ C2 ; :: thesis: S-bound S = min ((S-bound C1),(S-bound C2))
A2: S-bound C1 = lower_bound (proj2 .: C1) by Th44;
A3: S-bound C2 = lower_bound (proj2 .: C2) by Th44;
thus S-bound S = lower_bound (proj2 .: S) by Th44
.= lower_bound ((proj2 .: C1) \/ (proj2 .: C2)) by A1, RELAT_1:120
.= min ((S-bound C1),(S-bound C2)) by A2, A3, SEQ_4:142 ; :: thesis: verum