Trying to change the program so it can do better variable substition, thinking one way of doing this, is to explicitly define tiles in terms of rows,columns and colours - where rows, columns and colours are all facts. (As opposed to just colours, as was done previously). We might then be able to define some nicer rules in terms of what constitutes a diaganol - with the aim of trying to prolog to fill-in-blanks, when we ask it questions, rather than just 'yes', 'no....)