let a, b, c, d be Real; :: thesis: ( a <= b & c <= d implies W-bound (rectangle (a,b,c,d)) = a )

assume that

A1: a <= b and

A2: c <= d ; :: thesis: W-bound (rectangle (a,b,c,d)) = a

set X = rectangle (a,b,c,d);

reconsider Z = (proj1 | (rectangle (a,b,c,d))) .: the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) as Subset of REAL ;

A3: rectangle (a,b,c,d) = the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) by PRE_TOPC:8;

A4: for p being Real st p in Z holds

p >= a

p >= q ) holds

a >= q

.= lower_bound Z by PSCOMP_1:def 1

.= a by A4, A7, SEQ_4:44 ; :: thesis: verum

assume that

A1: a <= b and

A2: c <= d ; :: thesis: W-bound (rectangle (a,b,c,d)) = a

set X = rectangle (a,b,c,d);

reconsider Z = (proj1 | (rectangle (a,b,c,d))) .: the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) as Subset of REAL ;

A3: rectangle (a,b,c,d) = the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) by PRE_TOPC:8;

A4: for p being Real st p in Z holds

p >= a

proof

A7:
for q being Real st ( for p being Real st p in Z holds
let p be Real; :: thesis: ( p in Z implies p >= a )

assume p in Z ; :: thesis: p >= a

then consider p0 being object such that

A5: p0 in the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) and

p0 in the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) and

A6: p = (proj1 | (rectangle (a,b,c,d))) . p0 by FUNCT_2:64;

reconsider p0 = p0 as Point of (TOP-REAL 2) by A3, A5;

rectangle (a,b,c,d) = { q where q is Point of (TOP-REAL 2) : ( ( q `1 = a & q `2 <= d & q `2 >= c ) or ( q `1 <= b & q `1 >= a & q `2 = d ) or ( q `1 <= b & q `1 >= a & q `2 = c ) or ( q `1 = b & q `2 <= d & q `2 >= c ) ) } by A1, A2, SPPOL_2:54;

then ex q being Point of (TOP-REAL 2) st

( p0 = q & ( ( q `1 = a & q `2 <= d & q `2 >= c ) or ( q `1 <= b & q `1 >= a & q `2 = d ) or ( q `1 <= b & q `1 >= a & q `2 = c ) or ( q `1 = b & q `2 <= d & q `2 >= c ) ) ) by A3, A5;

hence p >= a by A1, A3, A5, A6, PSCOMP_1:22; :: thesis: verum

end;assume p in Z ; :: thesis: p >= a

then consider p0 being object such that

A5: p0 in the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) and

p0 in the carrier of ((TOP-REAL 2) | (rectangle (a,b,c,d))) and

A6: p = (proj1 | (rectangle (a,b,c,d))) . p0 by FUNCT_2:64;

reconsider p0 = p0 as Point of (TOP-REAL 2) by A3, A5;

rectangle (a,b,c,d) = { q where q is Point of (TOP-REAL 2) : ( ( q `1 = a & q `2 <= d & q `2 >= c ) or ( q `1 <= b & q `1 >= a & q `2 = d ) or ( q `1 <= b & q `1 >= a & q `2 = c ) or ( q `1 = b & q `2 <= d & q `2 >= c ) ) } by A1, A2, SPPOL_2:54;

then ex q being Point of (TOP-REAL 2) st

( p0 = q & ( ( q `1 = a & q `2 <= d & q `2 >= c ) or ( q `1 <= b & q `1 >= a & q `2 = d ) or ( q `1 <= b & q `1 >= a & q `2 = c ) or ( q `1 = b & q `2 <= d & q `2 >= c ) ) ) by A3, A5;

hence p >= a by A1, A3, A5, A6, PSCOMP_1:22; :: thesis: verum

p >= q ) holds

a >= q

proof

thus W-bound (rectangle (a,b,c,d)) =
lower_bound (proj1 | (rectangle (a,b,c,d)))
by PSCOMP_1:def 7
let q be Real; :: thesis: ( ( for p being Real st p in Z holds

p >= q ) implies a >= q )

assume A8: for p being Real st p in Z holds

p >= q ; :: thesis: a >= q

|[a,c]| in LSeg (|[a,c]|,|[b,c]|) by RLTOPSP1:68;

then A9: |[a,c]| in (LSeg (|[a,c]|,|[b,c]|)) \/ (LSeg (|[b,c]|,|[b,d]|)) by XBOOLE_0:def 3;

rectangle (a,b,c,d) = ((LSeg (|[a,c]|,|[a,d]|)) \/ (LSeg (|[a,d]|,|[b,d]|))) \/ ((LSeg (|[a,c]|,|[b,c]|)) \/ (LSeg (|[b,c]|,|[b,d]|))) by SPPOL_2:def 3;

then A10: |[a,c]| in rectangle (a,b,c,d) by A9, XBOOLE_0:def 3;

then (proj1 | (rectangle (a,b,c,d))) . |[a,c]| = |[a,c]| `1 by PSCOMP_1:22

.= a by EUCLID:52 ;

hence a >= q by A3, A8, A10, FUNCT_2:35; :: thesis: verum

end;p >= q ) implies a >= q )

assume A8: for p being Real st p in Z holds

p >= q ; :: thesis: a >= q

|[a,c]| in LSeg (|[a,c]|,|[b,c]|) by RLTOPSP1:68;

then A9: |[a,c]| in (LSeg (|[a,c]|,|[b,c]|)) \/ (LSeg (|[b,c]|,|[b,d]|)) by XBOOLE_0:def 3;

rectangle (a,b,c,d) = ((LSeg (|[a,c]|,|[a,d]|)) \/ (LSeg (|[a,d]|,|[b,d]|))) \/ ((LSeg (|[a,c]|,|[b,c]|)) \/ (LSeg (|[b,c]|,|[b,d]|))) by SPPOL_2:def 3;

then A10: |[a,c]| in rectangle (a,b,c,d) by A9, XBOOLE_0:def 3;

then (proj1 | (rectangle (a,b,c,d))) . |[a,c]| = |[a,c]| `1 by PSCOMP_1:22

.= a by EUCLID:52 ;

hence a >= q by A3, A8, A10, FUNCT_2:35; :: thesis: verum

.= lower_bound Z by PSCOMP_1:def 1

.= a by A4, A7, SEQ_4:44 ; :: thesis: verum