The Yff central triangle 
of a triangle 
is the innermost triangle determined
by the unique set of three isoscelizers for which
the four interior triangles 
, 
, 
, and 
are congruent (Kimberling 1998, pp. 94-95).
The three isoscelizers 
, 
, and 
are constructed one on each side and make all of
the inner triangles similar to each other.
It has trilinear vertex matrix
![[yz z(x+z) y(x+y); z(y+z) zx x(y+x); y(z+y) x(z+x) xy],](/images/equations/YffCentralTriangle/NumberedEquation1.svg) |
where 
,
,
and 
(Kimberling 1998, p. 172; typo corrected).
The original triangle 
is the extangents
triangle of the Yff central triangle 
.
The circumcircle of the Yff central circle is the Yff central circle.
The following table gives the centers of the Yff central triangle in terms of the centers of the reference triangle for Kimberling
centers 
with 
.
 | center of Yff central triangle |  | center of reference triangle |
 | Clawson point |  | congruent isoscelizers point |
 | Bevan point |  | incenter |
 | internal similitude center of circumcircle and incircle |  | Yff center of congruence |
 | orthocenter of the contact triangle |  | first mid-arc point |
