Let $$\mathfrak {f}= I-k$$
f
=
I
-
k
be a compact vector field of class $$C^1$$
C
1
on a real Hilbert space $$\mathbb {H}$$
H
. In the spirit of Bolzano’s Theorem on the existence of zeros in a bounded real interval, as well as the extensions due to Cauchy (in $$\mathbb {R}^2$$
R
2
) and Kronecker (in $$\mathbb {R}^k$$
R
k
), we prove an existence result for the zeros of $$\mathfrak {f}$$
f
in the open unit ball $$\mathbb {B}$$
B
of $$\mathbb {H}$$
H
. Similarly to the classical finite dimensional results, the existence of zeros is deduced exclusively from the restriction $$\mathfrak {f}|_\mathbb {S}$$
f
|
S
of $$\mathfrak {f}$$
f
to the boundary $$\mathbb {S}$$
S
of $$\mathbb {B}$$
B
. As an extension of this, but not as a consequence, we obtain as well an Intermediate Value Theorem whose statement needs the topological degree. Such a result implies the following easily comprehensible, nontrivial, generalization of the classical Intermediate Value Theorem: If a half-line with extreme$$q \notin \mathfrak {f}(\mathbb {S})$$
q
∉
f
(
S
)
intersects transversally the function$$\mathfrak {f}|_\mathbb {S}$$
f
|
S
for only one point of $$\mathbb {S}$$
S
, then any value of the connected component of$$\mathbb {H}{\setminus }\mathfrak {f}(\mathbb {S})$$
H
\
f
(
S
)
containingqis assumed by$$\mathfrak {f}$$
f
in$$\mathbb {B}$$
B
. In particular, such a component is bounded.