Subject: there are no squares with exactly three representations as the sum of two squares.
Subject: the order of Euclid’s propositions up to proposition 21.
Subject: replacement of Fano’s figure by cyclical pictures.
Subject: representations of numbers as sums of three squares.
Subject: constructing figures for finite geometries with the help of transpositions.
Subject: an example a transposition.
Subject: a reconstruction in first order logic.
Subject: solving queens problems with inductive and abductive inferences.
Subject: describing Iba’s macro operators for peg solitaire
Subject: a bucket of beautiful examples
Subject: solving Bertil Pouwels’ number puzzles without computer
Subject: imaginary configurations as parts of a given configuration in elementary mathematics
Subject: simple solutions for magical star and other problems.
Subject: pentagonal and heptagonal triangular numbers.
Subject: two dimensional pictures.
Subject: finding formulas.
Subject: representations as sums of squares.
Subject: representations as sums of squares simplified.
Subject: ‘seeing as’ and ‘replacing by’ in solving elementary mathematical problems.
Subject: simple solutions for magical star and other problems.
Subject: triangular square numbers.
Subject: finding representations as sums of two squares by successively elaborating the pairs with an odd sum.
Subject: representations of 139 as a sum of two squares.
Subject: changing problem domains
Subject: each natural number is the sum of three triangular numbers, including 0