import java.util.function.DoubleUnaryOperator;
import java.util.function.Function;
import static java.lang.Math.abs;
import static java.lang.Math.PI;

class Inverse {
    public static void main(String args[]) {
        Function<DoubleUnaryOperator, DoubleUnaryOperator> inverse =
            f -> x -> 1. / f.applyAsDouble(x);

	DoubleUnaryOperator cot = inverse.apply(Math::tan); // συνεφαπτομένη
	DoubleUnaryOperator sec = inverse.apply(Math::cos); // τέμνουσα
	DoubleUnaryOperator csc = inverse.apply(Math::sin); // συντέμνουσα

        final double EPSILON = 1e-15;
        assert abs(sec.applyAsDouble(0) - 1) < EPSILON;
        assert abs(csc.applyAsDouble(PI / 2) - 1) < EPSILON;
        assert abs(cot.applyAsDouble(PI / 4) - 1) < EPSILON;
    }
}