let a, b, d be Real; for p being Point of (TOP-REAL 2) st a <= b & p in LSeg (|[a,d]|,|[b,d]|) holds
( p `2 = d & a <= p `1 & p `1 <= b )
let p be Point of (TOP-REAL 2); ( a <= b & p in LSeg (|[a,d]|,|[b,d]|) implies ( p `2 = d & a <= p `1 & p `1 <= b ) )
assume that
A1:
a <= b
and
A2:
p in LSeg (|[a,d]|,|[b,d]|)
; ( p `2 = d & a <= p `1 & p `1 <= b )
thus
p `2 = d
by A2, TOPREAL3:12; ( a <= p `1 & p `1 <= b )
A3:
|[a,d]| `1 = a
by EUCLID:52;
|[b,d]| `1 = b
by EUCLID:52;
hence
( a <= p `1 & p `1 <= b )
by A1, A2, A3, TOPREAL1:3; verum