The course pact.
Try the exercise by hand first. Notice where you get stuck — that's the
learning. Only then ask the grader (or the hint button) to tell you
whether you're right. The tool is a sparring partner, not an oracle.
Welcome
If this is your first visit, register a display name and you'll receive
a 4-character handle. Keep your handle (paper memo, QR, or URL); you'll need
it to come back from another device.
Already have a handle? Open ?u=<handle> in your URL bar,
or use your QR / paper memo.