
Describes a “sandwich” constraint that does not imply uniqueness of all digits. The digits LittleSandwichConstraint.Digit1
and LittleSandwichConstraint.Digit2 must occur exactly once each (in any order) and form the edges of the sandwich. The
numbers sandwiched between them must sum up to LittleSandwichConstraint.Sum. 

Describes a constraint as used in Neighbor Sum Sudoku by Timwi
(https://logicmasters.de/Raetselportal/Raetsel/zeigen.php?id=0005NV): Each number outside the grid gives the sum
of all orthogonal neighbors of one cell in the corresponding row or column. Where multiple numbers are given, the
sums must be in the same order as the clues. 

Describes a “skyscraper sum” constraint: the numbers in the grid represent the height of a skyscraper; taller
skyscrapers obscure the view of smaller ones behind them; and the clue specifies the sum of the sizes of the
skyscrapers visible from the direction of the clue. This constraint implies a uniqueness constraint. 

Describes a constraint in a numberplacement puzzle. Two cells that are n steps from one another along the track
can’t both have the number n. The track is assumed to be a closed loop. 

Describes a “Ysum” constraint: the first Y numbers must sum up to a specified total, where Y is the Xth digit and
X is the first digit. This constraint implies a uniqueness constraint. 