theorem Thm20:
for
A,
B,
C being
Point of
(TOP-REAL 2) st
A,
B,
C is_a_triangle holds
(
angle (
A,
B,
C)
= (2 * PI) - (angle (C,B,A)) &
angle (
B,
C,
A)
= (2 * PI) - (angle (A,C,B)) &
angle (
C,
A,
B)
= (2 * PI) - (angle (B,A,C)) &
angle (
B,
A,
C)
= (2 * PI) - (angle (C,A,B)) &
angle (
A,
C,
B)
= (2 * PI) - (angle (B,C,A)) &
angle (
C,
B,
A)
= (2 * PI) - (angle (A,B,C)) )