theorem :: SIN_COS7:67

for x, y being Real holds
( not y = 1 / (((exp_R x) + (exp_R (- x))) / 2) or x = log (number_e,((1 + (sqrt (1 - (y ^2)))) / y)) or x = - (log (number_e,((1 + (sqrt (1 - (y ^2)))) / y))) )