# is odd?;

isodd(sin(x)):=true;
isodd(sinh(x)):=true;
isodd(erf(x)):=true;
isodd(x^n_):=If(isconstant(n) and isodd(n), true);
isodd(k_*x):=if(isconstant(k), true);
isodd(x):=true;