Method

This page will describe in detail how the problems are generated. Until then, in short:

• Each problem is built backwards from a known answer, its seed, by a list of rewriting steps, which are shown on the problem's page.
• The level is fixed by how the problem was built: textbook is one inverse step, medium two or three stacked rewrites, and gnarly four or more.
• Each problem has a method class, the kind of method its construction calls for, and is in one of 14 categories.
• The famous problems are collected from the literature, each with its status, solved, impossible or open, and who settled it, when, and where. An answer to an open problem that the checker finds right is reviewed by hand, and is never marked solved by the checker alone. A closed form of the impossible kind, for an impossible problem, is graded wrong.
• The checker grades each answer by evaluating it at test points, to high precision, against the known answer or the problem itself. Its output, the points, values, residuals and precision, can be downloaded for each answer and each run.