(ly:stencil-add
(make-filled-box-stencil xext (cons (- (car yext) thick) (car yext)))
(make-filled-box-stencil xext (cons (cdr yext) (+ (cdr yext) thick)))
(ly:stencil-add
(make-filled-box-stencil xext (cons (- (car yext) thick) (car yext)))
(make-filled-box-stencil xext (cons (cdr yext) (+ (cdr yext) thick)))