In a real Hilbert space
H
we consider a linear self-adjoint positive definite operator
A
:
V
=
D
(
A
)
⊂
H
→
H
and investigate
the behavior of the difference
u
−
v
of solutions to the problems
u
′′
(
t
) +
u
′
(
t
) +
Au
(
t
) =
f
(
t
)
, t >
0
,
u
(0) =
u
0
, u
′
(0) =
u
1
,
v
′
(
t
) +
Av
(
t
) =
f
(
t
)
, t >
0
,
v
(0) =
u
0
,
where
u
0
, u
1
∈
H, f
: [0
,
+
∞
)
→
H.
