See: List of castles Castles in England
Angus
Argyll and Bute
Dumfries and Galloway
Dundee
Edinburgh
Fife
Highland
Moray
Perthshire
Scottish Borders
Stirling
... can conveniently complete the square[?]. To "complete the square" is to add a constant (i.e., in this case, a quantity that does not depend on x) to the expression to the ...