let n, m be natural number ; for r being real number st not m is even & n >= m & r < 0 & r > - 1 holds
r to_power n >= r to_power m
let r be real number ; ( not m is even & n >= m & r < 0 & r > - 1 implies r to_power n >= r to_power m )
assume A0:
not m is even
; ( not n >= m or not r < 0 or not r > - 1 or r to_power n >= r to_power m )
assume A1:
n >= m
; ( not r < 0 or not r > - 1 or r to_power n >= r to_power m )
assume A2:
( r < 0 & r > - 1 )
; r to_power n >= r to_power m
zz:
n + 1 > m + 0
by A1, XREAL_1:10;
per cases
( n = m or n > m )
by zz, NAT_1:22;
suppose D2:
n > m
;
r to_power n >= r to_power mthen reconsider t =
n - m as
natural number by NAT_1:21;
C2:
(r to_power n) - (r to_power m) =
(r to_power (t + m)) - (r to_power m)
.=
((r to_power t) * (r to_power m)) - (1 * (r to_power m))
by JakPower32, A2
.=
((r to_power t) - 1) * (r to_power m)
;
C3:
r to_power m <= 0
by pom2, A2, A0;
D1:
t <> 0
by D2;
X:
abs r <= 1
by A2, ABSVALUE:12;
abs r <> 1
then H3:
abs r < 1
by X, XXREAL_0:1;
(
abs r > 0 &
t > 0 )
by D1, A2;
then
(abs r) to_power t < 1
to_power t
by H3, POWER:42;
then
(abs r) to_power t < 1
by POWER:31;
then
(
abs (r to_power t) < 1 &
r to_power t <= abs (r to_power t) )
by ABSVALUE:11, SERIES_1:2;
then
r to_power t < 1
by XXREAL_0:2;
then
(r to_power t) - 1
<= 1
- 1
by XREAL_1:11;
then
((r to_power n) - (r to_power m)) + (r to_power m) >= 0 + (r to_power m)
by C2, C3, XREAL_1:8;
hence
r to_power n >= r to_power m
;
verum end; end;