sin(-x_):= -sin(x); sin(0.5pi+x_):= cos(x); sin(-0.5*pi+x_):= -cos(x); sin(0.5pi-x_):= cos(x); sin(asin(x_)):=x; sin(pi) := 0; sin(2pi):=0; sin(3pi):=0; sin(-2pi):=0; sin(-3pi):=0; sin(2pi+x_):=sin(x); sin(-2pi+x_):=sin(x); sin(pi+x_):= -sin(x); sin(-pi+x_):= -sin(x); sin(1,0):=1;