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;