  Subjecting the SU(2) Yang--Mills system to azimuthal symmetries in both the
$x-y$ and the $z-t$ planes results in a residual subsystem described by a U(1)
Higgs like model with two complex scalar fields on the quarter plane. The
resulting instantons are labeled by integers $(m,n_1,n_2)$ with topological
charges $q=\frac12 [1-(-1)^m]n_1n_2$. Solutions are constructed numerically for
$m=1,2,3$ and a range of $n_1=n_2=n$. It is found that only the $m=1$
instantons are self-dual, the $m>1$ configurations describing composite
instanton-antiinstanton lumps.
