First Slip - find where your math working first went wrong

A math working marker. Type the problem and your working, one step per line - solving an equation, or simplifying, expanding or working out a value - and the page checks every line against the one before it, free, on a squared exercise-book page (equations by their solutions, expressions by their values). One metered run marks it like a teacher's red pen: a mark on every line (right, slip, follows on, note), a verdict by a fixed rule (full marks, one slip, see me, not finished), for each slip what went wrong, why and a nudge instead of the answer, the corrected first slipped line, done-well notes and one practice problem; the page re-checks the marks, solves the corrected line and the practice answer again, and checks your own answer to the practice problem for free. Built on @jmsktm/education-tutor.