placement of ties & slurs

[E. Hoffmann]

Hello together,

I am fairly new to lilypond, so it might well be that I just got confused in the
documentation which I appreciate, but find it sometimes difficult to
follow. Hope this question has not been answered a 100 times.

    When I insert ties or slurs, lilypond places them above or below.  Normally
this is right, but sometimes I want the tie or slur placed differently, just
like I can decide the direction of the stem  with \stemUp and \stemDown.

    I have a sheet music here, accordion, by an Adolf Götz, called "Hokuspokus".
There are chords like <a' e''>1 stretched over several bars.  It would be
helpful if I could place a slur above _and_ below those <a' e''>1 <a' e''>1 <a'
e''>1 &c.  Is this possible?

TIA Erich