let r be Real; :: thesis: for i being Integer st (2 * PI) * i <= r & r < ((3 / 2) * PI) + ((2 * PI) * i) holds
sin r > - 1
let i be Integer; :: thesis: ( (2 * PI) * i <= r & r < ((3 / 2) * PI) + ((2 * PI) * i) implies sin r > - 1 )
assume that
A1: ( H₁(i) <= r & r < ((3 / 2) * PI) + H₁(i) ) and
A2: sin r <= - 1 ; :: thesis: contradiction
A3: ( H₁(i) - H₁(i) <= r - H₁(i) & r - H₁(i) < (((3 / 2) * PI) + H₁(i)) - H₁(i) ) by A1, XREAL_1:9;
A4: sin r >= - 1 by Th3;
sin (r - H₁(i)) = sin (r + H₁( - i))
.= sin r by COMPLEX2:8
.= - 1 by A2, A4, XXREAL_0:1 ;
hence contradiction by A3, Th31; :: thesis: verum