Ключевые слова: abstract, adding, addition, affair, amount, arithmetic, background, banner, blackboard, blank, blankness, blunder, board, box, business, calculate, calculus, chalk, chalkboard, correct, decide, design, determine, dividing, division, education, equal, error, exclamation, failing, flat, fork, glass, gray shadow, grunge, hook, icon, interrogation, judge, judgment, label, lacunae, less, mark, mathematician, mistake, multiplication, multiply, no, operation, pattern, pick, pitchfork, plank, plus, problem, prong, proper, question, school, subtraction, tag, texture, triangle, unsolved, write, yes,