window-combined-p

window-combined-p is a compiled Lisp function in `window.el'.

(window-combined-p &optional WINDOW HORIZONTAL)

Return non-nil if WINDOW has siblings in a given direction.
WINDOW must be a valid window and defaults to the selected one.

HORIZONTAL determines a direction for the window combination. If
HORIZONTAL is omitted or nil, return non-nil if WINDOW is part of
a vertical window combination. If HORIZONTAL is non-nil, return
non-nil if WINDOW is part of a horizontal window combination.