Kure_RelationSetBit and Kure_RelationClearBit.
Both functions take four parameters, the manager, the relation, the
row, and the column.
If the parameters are valid (i.e. manager and relation are not NULL,
row and column are greater than 0 and less or equal than the height
and the width of relation), these functions return 1, otherwise 0.
To check, whether a pair is contained in a relation, there is the
function int Kure_RelationGetBit.
This function uses the same four parameters, but returns 0 if the
pair is not contained, 1 if the pair is contained, and -1 if an error
occured.